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Dolezal, Jiri,Song, Jong‐,Suk,Altman, Jan,Janecek, Stepan,Cerny, Tomas,Srutek, Miroslav,Kolbek, Jiri Springer Japan 2009 Ecological research Vol.24 No.2
<P><B>Abstract</B></P><P>Secondary woodlands in South Korea cover most mountains from low to middle elevations. While general patterns of forest succession are well understood, little is known about mechanisms of stand recovery after disturbance. We examined the spatio‐temporal variations in establishment, growth, size inequality, and mode of competition among trees in a 50‐year‐old post‐logging <I>Quercus mongolica</I>‐dominated stand. We further compared the growth and stem allometry of single trees, presumably of seed origin, with multi‐stemmed trees resprouting from stumps. <I>Q. mongolica</I> formed the upper canopy 16–22 m tall, 88.3% of total stand basal area, and 36.2% of total stem density, with most trees established during the first post‐logging decade (51.2% were resprouts). During the first three decades, the <I>Q. mongolica</I> recruits grew exponentially, and disproportionately more in diameter than few older reserved trees left after the last cutting. This substantially decreased size inequality. The reverse trend was observed from 1994 to 2004: larger trees grow more, indicating an increasing asymmetry of competition for light. Neighborhood analysis revealed that when target trees had more or larger neighbors, their exponential phase of growth was reduced and maximum size was decreased. After the 50 years of stand development, more than 70% of <I>Q. mongolica</I> showed growth decline as a result of competitive stress, and mortality was about 30%, concentrated in smaller size classes. Compared to single stems, resprouts within clones do not seem to compete less asymmetric as might be expected based on studies of clonal herbaceous plants and physiological integration within genets. As <I>Q. mongolica</I> was also negatively affected by competition from woody species currently prevailing in the lower tree stratum (<I>Tilia amurensis, Acer mono, Fraxinus rhynchophylla, Acer pseudosieboldianum</I>), we predict the stand will become increasingly dominated by these more shade‐tolerant trees.</P>
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Microstructure development of ultra fine grained Mg-22wt%Gd alloy prepared by high pressure torsion
Cizek, J.,Hruska, P.,Vlasak, T.,Vlcek, M.,Janecek, M.,Minarik, P.,Krajnak, T.,Slapakova, M.,Dopita, M.,Kuzel, R.,Kmjec, T.,Kim, J.G.,Kim, H.S. Elsevier Sequoia 2017 Materials science & engineering. properties, micro Vol.704 No.-
<P>A hardenable lightweight Mg-22 wt%Gd alloy with ultra fine grained (UFG) structure was prepared by high pressure torsion (HPT) at ambient temperature. The development of microstructure during HPT processing was investigated. A homogeneous UFG structure with grain size of 300 nm was achieved after 15 HPT revolutions. The UFG alloy exhibits enhanced strength due to work strengthening by tangled dislocations forming a dense forest throughout grains. Dislocation density in the sample was determined by positron annihilation spectroscopy (PAS) and X-ray line profile analysis (XLPA). It was found that there is an additional source of X-ray profile broadening in addition to small crystallites and micro-strains caused by dislocations. The additional micro-strain component was attributed to lattice modulation by Gd-rich nano-wires formed by agglomeration of Gd solutes and to strains arising from boundaries of crystallite domains and inter-domain interactions. Analysis of the influence of the crystallite size on the strength of UFG Mg-22 wt%Gd alloy revealed a breakdown in the HallPetch relationship when the crystallite size decreased below a critical value of approximate to 30 nm.</P>
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