Moisture Sorption Hysteresis and The Independent-domain Theory: The Moisture Distribution Function

To model the phenomenon of moisture sorption hysteresis using the independent domain theory, the moisture distribution among the domains must be established. This paper describes a procedure for obtaining such moisture distribution diagram from which may be calculated the moisture content of wood subjected to a series of relative humidity (RH) changes. The procedure is a refinement of the method described by the author in an earlier paper and is more consistent with the concept of independent domains. An alternative approach using numerical methods is also described

Experiments on Steady-State Nonisothermal Moisture Movement in Wood

The study was conducted to measure experimentally the steady-state uniaxial (tangential direction) moisture content and temperature profiles in moisture-sealed wood samples whose opposite faces were subjected to constant but different temperatures, and to compare these profiles with those predicted by several theoretical models. The experimental variables considered were wood species, initial moisture content, and temperature range.Opposite faces of the moisture-sealed assembly were exposed continuously for approximately five weeks to different but constant temperatures until the original uniform moisture content redistributed itself. At the steady state, a moisture content gradient opposite to the temperature gradient was established. The temperature gradient was constant in all cases, with the moisture content profile increasing almost exponentially with decreasing temperature. The absolute value of the ratio of the moisture content gradient to the temperature gradient (dM/dT)s was found to increase with wood moisture content and was observed to be higher at the higher temperature range. There was only a small difference in the -(dM/dT)s between the two species studied.The ratio -(dM/dT)s was analyzed in terms of five different theoretical models, two of which are based on nonequilibrium thermodynamics (NET) and three on classical thermodynamics. The two NET models (basic NET and Nelson models) provided the best agreement with the experimental values. The Siau model gave the next best prediction, followed by the Stanish model, and lastly by the Skaar-Siau model

Modeling Wood Moisture Sorption Hysteresis Based on Similarity Hypothesis. Part II. Capillary-Radii Approach

The applicability of Mualem's capillary-radii model to wood moisture sorption hysteresis is evaluated. The model further simplifies the prediction of sorption hysteresis in that scanning curves can be obtained from the moisture content and relative humidity data of the boundary isotherms, with no other intermediate parameters needed. A comparison of predicted moisture contents with actual experimental data points for yellow-poplar (Liriodendron tulipifera) indicates that the model consistently underestimates the primary desorption scanning isotherms, with errors ranging from -0.01 to -1.31. These prediction errors are slightly larger than those obtained from an earlier model based on Mualem's direct similarity hypothesis

Steady-State Diffusion of Chloropicrin in Douglas-Fir Heartwood

The effects of moisture content, flow direction, concentration, and temperature on the diffusion of chloropicrin in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) heartwood were investigated. Diffusion coefficients were strongly affected by wood moisture content. Coefficients for radial and tangential diffusion at the fiber-saturation point were twice as high as those at the oven-dry condition. Longitudinal diffusion coefficients, however, increased only 12.5% when the moisture content was increased over the same range. Longitudinal diffusion coefficients were about three orders of magnitude higher than those in the transverse directions, while there was no significant difference between radial and tangential diffusion coefficients. Diffusion coefficients were independent of concentration, showing the validity of Fick's law of diffusion in characterizing the flow of the fumigant in wood. Diffusion coefficients were always higher at 35 C than at 20 C; however, the difference was not statistically significant, suggesting that the flow of the fumigant is not a temperature-activated process

Unsteady-State Diffusion of Moisture In Giant Timber Bamboo (Phyllostachys Bambusoides Sieb. & Zucc.)

This paper presents the results of a study to determine the rate of moisture movement in giant timber bamboo (Phyllostachys bambusoides Sieb. & Zucc.) when exposed to three different temperatures (20 C, 30 C, and 40 C) at two ranges of moisture content (0 to 7.5%, and 7.5 to 15%). Edge-coated samples measuring 6 mm (R) x 30 mm (T) x 150 mm (L) were exposed to a given temperature-humidity combination in a conditioning chamber. The weight of a sample was continuously monitored over time and the weight-time data were analyzed using the Boltzmann solution to the unsteady-state form of Fick's diffusion equation.Diffusion coefficients ranged from 7.3 x 10~12 to 7.8 x 10~11 m2/sec. They were greater at the higher moisture content range. They increased with temperature such that the Arrhenius equation fits the data well, giving mean activation energies of 39,875 and 35,889 J/mole for the lower and higher moisture ranges, respectively. The calculated diffusion coefficient was approximately twice as high during desorption as during adsorption

Effect of Hardwood Vessels on Longitudinal Moisture Diffusion

The hypothesis that the longitudinal moisture content profile follows the shape of the sorption isotherm under steady-state diffusion condition was confirmed. This phenomenon was explained in terms of the unrestricted flow of water vapor from the lumen of one vessel element to the lumen of the next vessel element. Despite the assumed high vapor transport efficiency of the vessels, other cell types were believed to contribute substantially to longitudinal moisture movement. The diffusion coefficients of three different hardwood species were found to vary with moisture content

Technical Note: Shrinkage Properties of Partially Cad-Deficient Loblolly Pine Lumber

Partially cinnamyl alcohol dehydrogenase-deficient and wild-type loblolly pine (Pinus taeda) were studied for shrinkage properties. The study established no significant difference between these two genotypes. Results also showed that shrinkage of juvenile wood is significantly different from the corresponding shrinkage of mature wood only in the radial direction. Tangential shrinkage difference between juvenile and mature wood was significant when the uncorrected values were used but not when the true shrinkage values were used, thus highlighting the need to account for the effect of growth ring curvature on tangential shrinkage measurement of small-diameter trees

Steady-state diffusion of chloropicrin in Douglas-fir heartwood

The effects of moisture content, flow direction, concentration, and temperature on the diffusion of chloropicrin in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) heartwood were investigated. Diffusion coefficients were strongly affected by wood moisture content. Coefficients for radial and tangential diffusion at the fiber-saturation point were twice as high as those at the oven-dry condition. Longitudinal diffusion coefficients, however, increased only 12.5% when the moisture content was increased over the same range. Longitudinal diffusion coefficients were about three orders of magnitude higher than those in the transverse directions, while there was no significant difference between radial and tangential diffusion coefficients. Diffusion coefficients were independent of concentration, showing the validity of Fick's law of diffusion in characterizing the flow of the fumigant in wood. Diffusion coefficients were always higher at 35 C than at 20 C; however, the difference was not statistically significant, suggesting that the flow of the fumigant is not a temperature-activated process.Keywords: heartwood, diffusion, fumigant, Douglas-fir, chloropicri

Association of common ATM variants with familial breast cancer in a South American population

Background: The ATM gene has been frequently involved in hereditary breast cancer as a low-penetrance susceptibility gene but evidence regarding the role of ATM as a breast cancer susceptibility gene has been contradictory. Methods: In this study, a full mutation analysis of the ATM gene was carried out in patients from 137 Chilean breast cancer families, of which 126 were BRCA1/2 negatives and 11 BRCA1/2 positives. We further perform a case-control study between the subgroup of 126 cases BRCA1/2 negatives and 200 controls for the 5557G > A missense variant and the IVS38-8T > C and the IVS24-9delT polymorphisms. Results: In the full mutation analysis we detected two missense variants and eight intronic polymorphisms. Carriers of the variant IVS24-9delT, or IVS38-8T > C, or 5557G > A showed an increase in breast cancer risk. The higher significance was observed in the carriers of IVS38-8T > C (OR = 3.09 [95% CI 1.11-8.59], p = 0.024). The IVS24-9 T/(-T), IVS38-8 T/C, 5557 G/A composite genotype confered a 3.19 fold increase in breast cancer risk (OR = 3.19 [ 95% CI 1.16-8.89], p = 0.021). The haplotype estimation suggested a strong linkage disequilibrium between the three markers (D' = 1). We detected only three haplotypes in the cases and control samples, some of these may be founder haplotypes in the Chilean population. Conclusion: The IVS24-9 T/(-T), IVS38-8 T/C, 5557 G/A composite genotype alone or in combination with certain genetic background and/or environmental factors, could modify the cancer risk by increasing genetic inestability or by altering the effect of the normal DNA damage response