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Biodiversity and Regeneration of Canopy Tree Species in a Tropical Rain Forest in Southeast Asia
Kachi, N.,Okuda, Kachi N .,Yap, S . K .,Manokaran, N . 경북대학교 환경과학연구소 1995 環境科學硏究所論文集 Vol.9 No.1
Plants utilise basically the same resources, i.e. carbon dioxide, water, oxygen, and mineral nutrients, for their griwth and reproduction. If there are competitive differences among different plant species, ultimately only the most competitive species will expel the less competitive species. Then, why and how do so many kinds of plant species coexist in tropical rain forests? In addressing this question, two topics are presented from the viewpoint of plant population ecology. Basic data on biodiversity of a tropical rain forest in Southeast Asia are introduced, based on demographic data of a 50-ha permanent plot in Pasoh Forest Reserve. Malaysia. which was published by the Forest Research Institute of Malaysia. In this plot, there are ca. 335.000 individuals with a stem diameter 1 cm or larger at breast height and the total number of species is 814. Of these species. 366 are canopy or emergent tree species. This means that 45 of tree species diversity in this forest is maintained in the canopy layer. Populations of canopy tree species are maintained through the process of "gap regeneration". To identify fine-scale functional differences in response to a canopy gap among seedlings of canopy tree species, seedling growth and survival were compared between two common dipterocarp species (Shorea leprosula and Neobalanocarpus heimii) in a forest gap and unedr a closed canopy at Pasoh. In the gap. Shorea leprosula showed more enhanced growth and higher leaf turnover. Under the closed canopy, both species showed slow and comparable growth, but the survival rate of Shorea Ieprosula was lower. Higher seedling growth in a gap and lower survival under a closed canopy correspond to the higher turnover of the seedling or sapling bank of Shorea leprosula. In contrast, the slow and steady growth of Neobalanocarpus heimii, irrespective of light conditions, is consistent with the slow turnover of its sapling populations. Temporal and spatial variations in light environments during gap regeneration may cause suppression and release of seedling grewth. Regeneration of Shorea leprosula will be successful where gap formation is relatively frequent. whereas Neobalanocarpus heimii may regenerate at locations with infrequent gap formation. Based on these results. the implications of finescale partitioning of temporarily variable regeneration niches among different species for maintaining the species richness of tropical rain forests are discussed.
Prediction of the Rupture of Circular Sections of Reinforced Concrete and Fiber Reinforced Concrete
Adjrad, A.,Bouafia, Y.,Kachi, M.S.,Ghazi, F. Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3
As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section.
Prediction of the Rupture of Circular Sections of Reinforced Concrete and Fiber Reinforced Concrete
A. Adjrad,Y. Bouafia,M. S. Kachi,F. Ghazi 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.3
As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section.
Numerical Procedure for the Three-Dimensional Nonlinear Modelling of Composite Steel–Concrete Beams
Karim Benyahi,Youcef Bouafia,Marc Oudjene,Salma Barboura,Mohand Said Kachi 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.3
Composite steel–concrete structures are commonly used in the fi eld of bridges, where the steel frame provides great ease of installation, and concrete provides useful strength at low cost. This construction system makes it possible to seek to use each material to the best of its ability, so as to provide the entire construction system with greater savings. The purpose of this article is to be able to perform the simulation and the non-linear elastic calculation of composite steel–concrete beams through a calculation approach based on a matrix method of displacements. The numerical calculation model developed is based on taking into account the non-linearity of materials, or a set of laws allowing the modeling of the nonlinear behaviors of materials under an instantaneous and monotonous loading increasing until the ruin; the concrete is represented in its post-elastic part by a softening branch in compression and the contribution of the concrete stretched between two successive cracks is taken into account. Steel is represented by a perfect elastoplastic law or an elastoplastic law with fi rming. The proposed approach has been implemented on the Fortran programming language, where our procedure of numerical modeling of the mechanical behavior seems capable of correctly simulating the three-dimensional nonlinear behavior of isostatic and hyperstatic composite steel–concrete beams, under monotonous (increasing) static loading until ruin. It was validated by comparing the results of our calculations to experimental results or to analytical solutions.
( Hiroyasu Iwasaki ),( Takashi Mizushima ),( Yuta Suzuki ),( Shigeki Fukusada ),( Kenta Kachi ),( Takanori Ozeki ),( Kaiki Anbe ),( Hironobu Tsukamoto ),( Fumihiro Okumura ),( Takashi Joh ),( Hitoshi 대한소화기학회 2017 Gut and Liver Vol.11 No.1
Background/Aims: Self-expandable metallic stent (SEMS) placement is effective for dysphagia that results from malignant obstruction of the esophagus or gastric cardia; however, stent-related complications may be life-threatening. Thus, the goal of this study was to identify risk factors associated with complications following esophageal stenting. Methods: Of the 71 patients who underwent SEMS placement for dysphagia as a result of malignant stricture of the esophagus or gastric cardia, 53 patients with squamous cell carcinoma or adenocarcinoma, without previous SEMS placement, without a fistula, and without recurrent tumor after surgery were retrospectively identified. The occurrence of stent-related complications was used as an endpoint. Results: Stentrelated complications were identified in 26 patients (49.1%), and major complications occurred in 14 patients (26.4%). The use of an Ultraflex stent (odds ratio [OR], 6.81; 95% confidence interval [CI], 1.54 to 30.00; p=0.011) and prior chemotherapy (OR, 6.13; 95% CI, 1.46 to 25.70; p=0.013) were significantly associated with stent-related complications. Moreover, the use of an Ultraflex stent (OR, 19.60; 95% CI, 2.26 to 170.00; p=0.007) and prior radiation (OR, 25.70; 95% CI, 2.37 to 280.00; p=0.008) significantly increased the risk of major complications. Conclusions: The use of an Ultraflex stent and prior radiation and/or chemotherapy may represent risk factors for complications following esophageal SEMS placement. (Gut Liver 2017;11:47-54)