Investigation of wood properties that influence the final moisture content of air-dried sugi (Cryptomeria japonica) using principal component regression analysis
Sugi (Cryptomeria japonica D. Don) lumber is known to have a large variability in final moisture content (MCf) and is difficult to dry. This study investigated the variability in MCf of sugi in relation to wood properties. The wood property variables included initial moisture content (MCi), basic density (BD), annual ring orientation (ARO), annual ring width (ARW), heartwood ratio (HR) and CIE L* color (L*). Sugi samples were cut from flat-sawn lumbers and air-dried; a principal component regression (PCR) model for predicting MCf was developed with the wood property variables. The wood properties that contributed to the prediction of MCf were evaluated by PCR analysis. Significant positive regression coefficients of the PCR model were observed in the MCi, BD, ARO and HR, whereas negative ones in the L*. There were no significant regression coefficients in the ARW. These results suggest that the MCi, BD, ARO and HR had a positive influence, the L* had a negative influence, and the ARW had little influence on the MCf of air-dried sugi wood. This finding is in line with the general view on the drying characteristics in relation to these wood properties.
The effect of drying schedule on the radial permeability ofPinus radiata D. Don
The effect of air-,kiln-, and high-temperature drying on the radial permeability ofPinus radiata D. Don was studied. It was found that for both heartwood and sapwood the permeability increased as the severity of drying increased. The sapwood permeability rose from 5.3×10−14m2 for air-dried timber to 10.9×10−14 m2 for high-temperature-dried timber, an increase of approximately 100%. The rise in heartwood permeability was approximately 280%, with the air-dried permeability being 1.3×10−14 m2 and the high-temperature-dried permeability being 5.3×10−14 m2. It is considered that this higher radial permeability of high temperature-dried wood is responsible for its increased ease of impregnation with preservatives. As the predominant route for gas movement inP. radiata is the resin canal network, it is suggested that this increase in permeability is due to movement and modification of the resin. The flow through the samples was entirely laminar, with no evidence of either molecular or turbulent flow for pressure differentials from 10 to 100 kPa.ZusammenfassungDer Einfluß von Luft-, Ofen- und Hochtemperatur-Trocknung auf die radiale Durchlässigkeit von Kiefernholz wurde untersucht. Sowohl im Kernholz als auch in Splintholz stieg die Durchlässigkeit mit der Trocknungsschärfe an. Im Splintholz stieg die Durchlässigkeit um 100% von 5,3×10−14 m2 bei luftgetrocknetem Schnittholz auf 10,9×10−14 m2 nach Hochtemperatur-Trocknung. Diese nach Hochtemperatur-Trocknung erhöhte Durchlässigkeit wird als Ursache für die leichtere Tränkbarkeit diese Proben mit Holzschutzmitteln angesehen. Weil die Hauptbewegung des Wassers als gas durch die Harzkanäle erfolgt, ist anzunehmen, daß die erhöhte Durchlässigkeit durch Verlagerung und Veränderung der Harze bedingt ist. Der Gasfluß durch die Proben war völlig laminär ohne irgendwelche Anzeichen von molekulare oder turbulenter Strömung für Druckunterschiede zwischen 10 und 100 kPa.
Fieldwork in geography teaching: A critical review of the literature and approaches
Abstract Virtually all lecturers in geography recognise the importance of fieldwork as a vital mode of teaching in the subject. This paper draws on material produced as part of a HEFCE review of teaching and learning in the field and assesses the implications of recent changes in higher education for field studies in geography. The literature on the development of, and recent changes in, fieldwork practice is reviewed and assumptions about appropriate forms of teaching and assessment are challenged. The need for carefully integrated preparation of project‐orientated fieldwork is stressed and the importance of debriefing and feedback after field visits is emphasised. Various suggestions for guidelines on good practice are presented. Finally, a range of future issues and problems in fieldwork is identified and discussed.