Sandwich compression of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) wood: density distribution, surface hardness and their controllability

The sapwood and heartwood of plantation sugi wood (Cryptomeria japonica), and plantation hinoki (Chamaecyparis obtusa) wood were flat-sawn into timbers, then kiln-dried to a MC level below 12%. These timbers were further processed into specific sizes and wetted on the surfaces, preheated at 150 °C and radially compressed into sandwich compressed timbers. Density distribution, compressed layer(s) position and thickness, surface hardness were investigated. It was demonstrated that sugi and hinoki timbers were both applicable for sandwich compression. By controlling the preheating time, sugi heartwood timber, sugi sapwood timber and hinoki timber can be all sandwich compressed, which resulted in surfaces compressed timbers, interior compressed timbers and center compressed timbers. When sugi timbers were sandwich compressed, density only tremendously increased in the earlywood. The increased density of the compressed sugi earlywood was independent of compressed layer(s) position, compressing distance or annual growth width, while for hinoki timbers compression, density increased both in earlywood and latewood. Surface hardness of the uncompressed sugi sapwood was almost twice of that of the uncompressed sugi heartwood. Surface compression sharply increased the surface hardness of sugi heartwood and sugi sapwood. Interior compression and center compression also contributed to increased surface hardness for the compressed timbers, but to smaller extents. Surface hardness change due to the surface compression was consistent with the surface average density change of timbers. Compression layer(s) position exerted statistically significant effects on the surface hardness, while surface hardness of the compressed wood was almost unrelated to the original density of the used wood or average density of the sandwich compressed wood. However, bigger compressing distance led to bigger surface hardness for the surface compressed wood.

Ionising feedback from an O star formed in a filament

We explore a simple semi-analytic model for what happens when an O star (or cluster of O stars) forms in an isolated filamentary cloud. The model is characterised by three configuration parameters: the radius of the filament, $R_{_{\rm FIL}}$, the mean density of H2 in the filament, $n_{_{\rm FIL}}$, and the rate at which the O star emits ionising photons, $\dot{\cal N}_{_{\rm LyC}}$. We show that for a wide range of these configuration parameters, ionising radiation from the O star rapidly erodes the filament, and the ionised gas from the filament disperses into the surroundings. Under these circumstances the distance, L, from the O star to the ionisation front (IF) is given approximately by L(t) ∼ 5.2 pc$\, [R_{_{\rm FIL}}/0.2\, {\rm pc}]^{-1/6}$$\, [n_{_{\rm FIL}}/10^4\, {\rm cm^{-3}}]^{-1/3}$$\, [\dot{\cal N}_{_{\rm LyC}}/10^{49}\, {\rm s}^{-1}]^{1/6}$ [t/Myr]2/3, and we derive similar simple power-law expressions for other quantities, for example the rate at which ionised gas boils off the filament, $\dot{M}_{_{\rm IF}}(t)$, and the mass, $M_{_{\rm SCL}}(t)$, of the shock-compressed layer (SCL) that is swept up behind the IF. We show that a very small fraction of the ionising radiation is expended locally, and a rather small amount of molecular gas is ionised and dispersed. We discuss some features of more realistic models, and the extent to which they might modify or invalidate the predictions of this idealised model. In particular we show that, for very large $R_{_{\rm FIL}}$ and/or large $n_{_{\rm FIL}}$ and/or low $\dot{\cal N}_{_{\rm LyC}}$, continuing accretion onto the filament might trap the ionising radiation from the O star, slowing erosion of the filament even further.

The relationship between the hydrothermal response of yield stress and the formation of sandwich compressed wood

The effects of yield stress of poplar ( Poplar × euramericana cv. ‘Neva’) on temperature (60–210°C), moisture content (oven dry-30%) and grain response mechanism and as well as its role in the formation of sandwich compressed wood were studied in this paper. The results showed that the yield stress of wood was significantly affected by moisture content(MC), temperature and their interaction. Compared with temperature, the relative change rate of yield stress was nearly 10 times higher for each 1% increase in MC than for each 1°C increase in temperature. The experimental data revealed that the relative change rate of yield stress depended on the softening effect of wood by moisture and temperature. The asymmetry of yield stress in different grain direction also depended on wood hydrothermal softening effect. Raising the temperature or increasing the MC could make wood radial vs tangential asymmetry decrease and radial vs radial tangential asymmetry disappear. In the process of hydrothermal compression, the yield stress gradient caused by the hydrothermal softening inside the wood was the main reason for the formation of sandwich compressed wood, and provided a scientific basis for the controllability of the position and thickness of the compressed layer(s).

The role of magnetic field in the formation and evolution of filamentary molecular clouds

Recent observations have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of molecular cloud cores by the gravitational fragmentation of filamentary molecular clouds. In this review we summarize our current understanding of various processes that are required in describing the filamentary molecular clouds. Especially we can explain a robust formation mechanism of filamentary molecular clouds in a shock compressed layer, which is in analogy to the making of “Sushi.” We also discuss the origin of the mass function of cores.