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    Abstract

    Color changes of four softwood and seven hardwood species during hygrothermal treatment were compared among species and kinetically evaluated. Treatment temperature ranged from 70 to 120 °C, and the durations were 5–150 h. Generally, the \(L^{*}\) (lightness) decreased and the total color differences \((\Delta E_{\text{ab}}^{*})\) increased irrespective of the treatment temperature. \(a^{*}\) and \(b^{*}\) (redness and yellowness) values varied spuriously based on the wood species. Kinetic analysis using the time–temperature superposition principle, which uses the whole data set, was successfully applied to the color changes. The apparent activation energies of the color changes calculated from \(\Delta E_{\text{ab}}^{*}\) were 24.3–40.8 kJ/mol for softwood and 32.3–61.3 kJ/mol for hardwood. The average apparent activation energy for hardwood was higher than for softwood. These values were lower than those calculated from other material properties. The obtained results will contribute to assess the color changes during the early stage of kiln drying and hygrothermal modification of wood.


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    Abstract

    Hygrothermal recovery (HTR), the dimensional changes in wood induced by hygrothermal treatment, was investigated using both compression and normal wood of sugi (Cryptomeria japonica). The elastic released strain of growth stress was measured on living tree surfaces; subsequently, the specimens were taken from the same position to measure HTR. HTR was measured as dimensional changes due to treatment at 20, 40, 60, 80, and 100 °C in hot water ranging from 200 min to 177 days. The intensity of HTR had a positive relationship with elastic released strain of growth stress. This result suggests that HTR is the relaxation of the viscoelastic component of growth stress accumulated during the maturation process of trees. The rate of HTR clearly showed a time–temperature dependency: higher at higher treatment temperatures and lower at lower treatment temperatures. Based on kinetic analysis, the apparent activation energy (Ea) was calculated as 407 kJ/mol, which is similar to the published Ea of lignin softening implying that the HTR is a lignin-related phenomenon.


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    Abstract

    When a green wood specimen is hygrothermally treated, it often shows dimensional changes in the longitudinal and transversal directions, which is called hygrothermal recovery of wood. Hygrothermal recovery of tension wood is assumed to be behind the unusual contraction of gelatinous layer along the longitudinal axis. This study investigated whether hygrothermal recovery of tension wood was temperature-dependent. Hygrothermal treatment at 80, 100 and 120 °C was given to green Quercus serrata tension wood, and longitudinal and tangential dimensions were recorded. In the longitudinal direction, the trend line obtained after 10 times of 10-min hygrothermal treatments at respective temperatures unraveled that it was comprised of initial recovery and continuum contraction at 100 and 120 °C, but no initial recovery was recognized at 80 °C. In the tangential direction, both the initial and the continuum deformations were expansive, and initial recovery was smaller at 80 °C. The results of multiple comparison test revealed that the parameters characterizing the trend line differed significantly among three temperature sets. Further, the result highlighted the existence of breakage of hygrothermal recovery mechanism at temperature between 80 and 100 °C.


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    Abstract

    Preventing falls is one of the clinical problem and causes patients’ significant problem, since it may cause serious injuries such as an abrasion and fractures. An assessment score sheet for inpatients is one of the falls prevention system. In this paper, we focus on sheet for inpatients’ fall risk. In this paper, we validate the appropriateness of the falls estimate in patients hospitalising. We reassessed the score of 84 cases which consist of 42 sets of the actual patient data for patients who have fallen and 42 sets of the data for those who have not from seven wards from October 2013. The results showed four items as greatly influence the falls. With these items, we calculated fall probabilities of each patients, and compared them of patients who have fallen and those who have not. Then, we could not recognise the difference between two groups since the number of people whose probability of fall is more than 60% are 34 cases in patients who fallen and 24 cases who did not fall. From the result of the analysis, we discuss it is not enough that nurses estimate the patient’s fall risk only using the assessment in patients at the time of hospitalising. Instead, the importance of daily assessment is shown.


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    Abstract

    The delayed recovery of the longitudinal length in biomechanically pre-stressed wood, specifically tension wood with a conspicuous gelatinous layer in the cell wall structure, was generally induced by hygrothermal treatment. However, hygrothermal treatment should not be the sole method to induce delayed recovery in tension wood. In order to broaden our understanding of the mechanism underlying delayed recovery, tension wood of Quercus serrata was treated by drying and subsequent rewetting over many times. Interestingly, the longitudinal deformation over repeated drying and subsequent rewetting treatments (dry–wet treatments) was identical to the response of the tension wood during repetitive hygrothermal treatments. Hence, the longitudinal delayed recovery in pre-stressed tension wood was concluded to be induced not only by hygrothermal treatment but also by the dry–wet cycles.


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    Abstract

    To clarify the mechanism of irreversible dimensional changes due to the hygrothermal treatment of green wood, i.e., the hygrothermal recovery (HTR), the changes in vibrational properties of compression wood and normal wood were measured after hygrothermal treatment at 60 °C, 80 °C, and 100 °C. In addition, the relationship between those changes and HTR strains were discussed. The hygrothermal treatment induced an increase in mechanical loss tangent (tanδ) and decrease in specific dynamic Young’s modulus (E). It seems that the changes in vibrational properties due to hygrothermal treatment had a time–temperature dependency: Higher temperatures and longer treatment durations induce larger increases in tanδ and larger decreases in E′/ρ. In contrast to the quenching effect, tanδ and E′/ρ did not recover to their original state even after 60 days of conditioning in water at 20 °C. For compression wood with a large microfibril angle (MFA), there was a clear relationship between the changes in vibrational properties and HTR strains. The tanδ increased and E decreased with hygrothermal treatment, corresponding to dimensional changes in the L-direction. This suggests that structural changes in wood components are responsible for HTR. The most likely mechanism for HTR is that the hygrothermal treatment softens the lignin to release locked-in growth stress. Subsequently, irreversible structural changes in lignin induce both the changes in vibrational properties and HTR. For normal wood, because of the small MFA, the structural changes in lignin in the L-direction are possibly restricted by crystalline cellulose. As a result, the relationship between the changes in vibrational properties and HTR is uncertain.


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