Numerical and experimental study of moisture-induced stress and strain field developments in timber logs

When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.     

Finite element study of growth stress formation in wood and related distortion of sawn timber

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.     

EDTA-Enhanced Phytoremediation of Lead-Contaminated Soil by Corn

EDTA-enhanced phytoremediation by corn (Zea mays L.) of soil supplemented with 500 mg L^?1 lead (Pb) was examined. The chelate EDTA was used in order to increase Pb bioavailability at four levels: 0 (control), 0.5 (low), 1.0 (medium), and 2.5 mmol kg^?1 (high). Plants were grown under controlled conditions in a growth-chamber with supplementary light. An EDTA concentration of 5.0 mmol kg^?1 was lethal to plants. At high and medium EDTA levels plants grew significantly less than control ones. Lead concentrations in corn leaves increased with increased EDTA levels. Plants subjected to medium EDTA level had the greatest root to shoot Pb translocation. Plants subjected to high EDTA level showed high phosphorus (P) uptake and translocation within plants. Therefore, possibly it was not only Pb that caused toxic effect on plants, but also the high internal concentration of P that in turn could have complexed active Fe.     

Large-scale reclamation of barren lands in Iceland by aerial seeding

Catastrophic soil erosion has resulted in the desertification of vast areas in Iceland. Barren lands are revegetated on a large scale by aerial broadcasting of commercial grass seed of Festuca rubra cv. Leik (red fescue) and subsequent regular fertilizer application for five years. Vegetation cover following aerial seeding of F. rubra was recorded in three reclaimed sites, which were two, ten and 25 years old, in an inland area in southern Iceland. As a comparison, vegetation cover was also recorded on barren land. Plant succession was inferred from these records. Vegetation cover was recorded using the point-intercept method. Spores of arbuscular mycorrhizae fungi (AMF) were recorded from each site. Barren lands have characteristically low (<5%) vegetation cover. The highest cover of F. rubra was found two years after revegetation was initiated. Non-dependent AMF forbs also colonized and increased their cover rapidly in the second year due to fertilizer application, but after a decade their cover declined. Ten years after the aerial seeding, F. rubra disappeared and the area was dominated by the native grass Agrostis stolonifera (creeping bent grass). A cover of mosses and plant litter was also recorded on the ten-year-old site. AMF spores were low in all studied sites, and colonization of AMF was only found in the roots of A. stolonifera. After 25 years, it appeared that the cover of native forbs started to increase again and salix bushes were established. Aerial seeding of F. rubra failed to create a long-lasting cover to facilitate natural rapid succession. Alternative revegetation practices, taking into consideration the dynamics of the mutualistic microorganisms (Rhizobium and AMF)/plant association, are suggested for a better and more economic management of reclamation strategies. Copyright © 1999 John Wiley & Sons, Ltd.     

Atipamezole in the management of detomidine overdose in a pony

OBSERVATIONS: A pony undergoing elective castration accidentally received an overdose of IV detomidine (200 microg kg(-1)) before anaesthesia was induced with ketamine and midazolam. A further 100 microg kg(-1) IV dose of detomidine was administered during anaesthesia. The mistake was recognized only when the animal failed to recover from anaesthesia in the expected time. The overdose (300 microg kg(-1) in total) was treated successfully with atipamezole, initially given IV and subsequently IM and titrated to effect to a total dose of 1100 microg kg(-1). The pony regained the standing position. A further injection of atipamezole (76 microg kg(-1) IM) was given 5 hours later to counteract slight signs of re-sedation. CONCLUSIONS: Atipamezole proved an effective antagonist for detomidine in a pony at an initial dose 3.65 x and a final total dose 3.9 x greater than the alpha2 agonist.     

Pedogenesis and weathering rates of a Histic Andosol in Iceland: Field and experimental soil solution study

It is important to study the rate determining processes of chemical weathering and soil formation in volcanic islands since a significant part of the carbon fixed by chemical weathering of silicates on Earth is fixed at the surface of volcanic islands. These soils are fertile and much of the river suspended matter delivered to the ocean stems from these islands. This study determines the factors that drive the pedogenesis of a Histic Andosol in Western Iceland. Soil solutions were extracted from the profile in the field, from undisturbed ex situ mesocosms and from repacked laboratory microcosms. Concentrations of measured and calculated inorganic species in the field and experimental soil solutions were used for thermodynamic and kinetic interpretation, and to calculate the weathering rates.

The main primary rock constituent of the 205 cm thick soil profile was basaltic glass, allophane content ranged from 2 to 22% and the soil carbon content ranged from 11 to 42%. Mean soil solution pH value ranged from 4 to 6 with the lowest value at 80 cm depth and highest between 150 to 205 cm. The high solute concentrations in soil solutions in the beginning of the microcosm weathering experiment declined faster for anions than cations. Under field conditions inorganic anions were supplied by marine and anthropogenic rather than pedogenic sources and hence these anions were subsequently leached out during the experimental duration when there was a limited input of anions through experimental precipitation. The factor, which defined the rate at which each ion was depleted from the exchange complex of the soil, decreased down the soil profile. The release sequence at 50 cm depth was Cl > Na > SO₄ > F > Si. The Si and base cations experimental weathering rate when normalized to geographical surface area are similar to or lower than those measured from river catchments in Southwestern Iceland. The dissolved Al flux was much higher from the soil when compared to the river catchments.

Field and experimental soil solutions were all highly undersaturated with respect to basaltic glass. Field and mesocosm samples were supersaturated with respect to secondary allophane and imogolite, while samples from the microcosms were often undersaturated with respect to allophane and imogolite. Predicted dissolution rate was dictated by the soil solution aH+3/aAl3+ activity ratio but slowed down by up to 20% and 30% by decreasing undersaturation in field and mesocosms respectively. Predicted dissolution rates according to the aH+3/aAl3+ activity ratio increased up to factor of 7, 30 and 37 by speciating Al3+ with oxalate in field, mesocosms and microcosms respectively. Speciation with oxalate, which represents the maximum effect of the dissolved organic carbon (DOC) on dissolution rates, generally had more effect near the surface than at deep levels in the soil profile. This study shows that at fixed temperature, reactive surface area, and composition of the volcanic glass in the soil, the chemical weathering rates of Andosols are dictated by: 1) aeolian deposition rates and drainage, which affect the saturation state and the aH+3/aAl3+ activity ratio, 2) the production of organic anions within the soil, and 3) external supply of anions capable of complexing Al3+.     

Effect of iron plaque on roots of rice on growth of plants in excess zinc and accumulation of phosphorus in plants in excess copper or nickel

Iron (Fe) plaque on roots of rice was found to lessen the toxic effects of zinc (Zn). With excess Zn, plants with Fe plaque had significantly greater dry mass of roots and foliage than plants without plaque. In the excess of Zn, plants with Fe plaque had higher concentrations of Fe but lower Zn than plants without plaque, although the differences were not significant. In the excess of copper (Cu) or nickel (Ni), plants with Fe plaque had significantly lower concentration of phosphorus (P) in leaves than plants without plaque. It is suggested that the low concentration of P in leaves of plants with plaque will increase the concentration of “active iron”; inside leaves, and therefore, increase their tolerance against heavy metal toxicity.     

Effects of temperature and dietary n-3 and n-6 fatty acids on endocytic processes in isolated rainbow trout (Oncorhynchus mykiss,Walbaum) hepatocytes

Effects of different incubation temperatures (2, 8, 14 and 20°C) and hepatocyte membrane fatty acid composition on the rate of internalization and lysosomal degradation of the ligand, mannosylated albumin, that is taken up by receptor-mediated endocytosis, were investigated in rainbow trout (Oncorhynchus mykiss, Walbaum). The fish were kept at a water temperature ranging from 9 to 14°C and fed pelleted diets coated with either capelin oil (control), EPA/DHA-concentrate (rich in n-3 polyunsaturated fatty acids) or soybean oil (rich in n-6 unsaturated fatty acids) for at least 3 months prior to sampling. The endocytic uptake mediated by the mannose receptor was very efficient at all temperatures studied. Lysosomal degradation, on the other hand, came to a halt below 8°C. The activation energies for uptake and degradation were 54.6 and 164.2 kJ/mol respectively. No negative effects of increased amounts of either n-3 or n-6 fatty acids were observed on the endocytic parameters studied. On the contrary, multivariate analysis indicated a positive relationship between high levels of n-6 fatty acids and low unsaturation index in the phosphatidylcholine (PC) fraction of the hepatocytes and the internalization rate of 2°C, meaning that the rate of receptor-mediated endocytosis may be affected by membrane fatty acid composition.