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- 저자 : 이승혁 (검색결과 192 건)
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용탕단조법으로 제조된 AZ91-X (Y, Nd, Sr) 합금의 미세파괴기구
이승혁,이성학,김도향 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.5
A study was made of the effects of alloying elements on the microstructure and microfracture mechanism of squeeze cast AZ91-X(X=Y, Sr, Nd) magnesium alloys. Particular emphasis was placed on the role of Y and Nd, which are important alloying elements in magnesium alloys fabricated by rapid solidified process. Microstructural observation, in situ fracture test, and fractographic observation were conducted on the alloys to clarify the microfracture process. Microstructural analyses indicated that the grain refinement could be achieved by small addition of alloying elements, although Mg_(17)Al_(12) phases were still present along grain boundary. From in situ observation of the AZ-Sr alloy, coarse needle-shaped particles and Mg_17)Al_(12) phases located along grain boundary provided easily intergranular fracture sites under low stress intensity factor levels, resulting in the drop in toughness. In the AZ-Y and the AZ-Nd alloys, on the other hand, a number of planar slip bands and twinnings were well developed inside grains, thereby leading to the enhancement of overall mechanical properties. These findings indicated that small addition of Y or Nd was very effective in improving mechanical properties on the basis of the well-developed twinnings and slip bands.
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Budget and distribution of organic carbon in Quercus serrata Thunb. ex Murray forest in Mt. Worak
이승혁,장래하,조규태,유영한 한국생태학회 2015 Journal of Ecology and Environment Vol.38 No.4
The carbon cycle came into the spotlight due to the climate change and forests are well-known for their capacity to store carbon amongst other terrestrial ecosystems. The annual organic carbon of litter production, forest floor litter layer, soil, aboveground and belowground part of plant, standing biomass, net primary production, uptake of organic carbon, soil respiration, etc. were measured in Mt. Worak in order to understand the production and carbon budget of Quercus serrata forest that are widely spread in the central and southern part of the Korean Peninsula. The total amount of organic carbon of Q. serrata forest during the study period (2010-2013) was 130.745 ton C ha-1. The aboveground part of plant, belowground part of plant, forest floor litter layer, and organic carbon in soil was 50.041, 12.510, 4.075, and 64.119 ton C ha-1, respectively. The total average of carbon fixation in plants from photosynthesis was 4.935 ton C ha-1 yr-1 and organic carbon released from soil respiration to microbial respiration was 3.972 ton C ha-1 yr-1. As a result, the net ecosystem production of Q. serrata forest estimated from carbon fixation and soil respiration was 0.963 ton C ha-1 yr-1. Therefore, it seems that Q. serrata forest can act as a sink that absorbs carbon from the atmosphere. The carbon uptake of Q. serrata forest was highest in stem of the plant and the research site had young forest which had many trees with small diameter at breast height (DBH). Consequentially, it seems that active matter production and vigorous carbon dioxide assimilation occurred in Q. serrata forest and these results have proven to be effective for Q. serrata forest to play a role as carbon storage and NEP. carbon of Q. serrata forest during the study period (2010-2013) was 130.745 ton C ha-1. The aboveground part of plant, belowground part of plant, forest floor litter layer, and organic carbon in soil was 50.041, 12.510, 4.075, and 64.119 ton C ha-1, respectively. The total average of carbon fixation in plants from photosynthesis was 4.935 ton C ha-1 yr-1 and organic carbon released from soil respiration to microbial respiration was 3.972 ton C ha-1 yr-1. As a result, the net ecosystem production of Q. serrata forest estimated from carbon fixation and soil respiration was 0.963 ton C ha-1 yr-1. Therefore, it seems that Q. serrata forest can act as a sink that absorbs carbon from the atmosphere. The carbon uptake of Q. serrata forest was highest in stem of the plant and the research site had young forest which had many trees with small diameter at breast height (DBH). Consequentially, it seems that active matter production and vigorous carbon dioxide assimilation occurred in Q. serrata forest and these results have proven to be effective for Q. serrata forest to play a role as carbon storage and NEP.
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이승혁,유영한 한국생태학회 2012 Journal of Ecology and Environment Vol.35 No.3
Quercus aliena and Q. serrata are both occur as natural vegetation alongside natural freshwater bodies of the southern Korea Peninsula. Q. serrata dominates over Q. aliena as secondary forest vegetation in the present day. In order to explain these natural distributional traits of the oak species, we conducted some experiments with oak seedlings which treated with major important environmental resources, including light, moisture and nutrients, under controlled conditions. We then measured the ecological niche breadths and overlap from 15 eco-morphological characteristics. The ecological niche breadth of Q. aliena and Q. serrata were higher in terms of the nutrient factor applied, but was lower terms of light. The niche breadth of Q. serrata was wider than that of Q. aliena in light and moisture exposure. On the other hand, the niche breadth of Q. aliena was similar with that of Q. serrata in terms of the nutrient factor applied. These results imply that Q. serrata has a broader ecological distribution in over a wider variety of light and moisture environments than that of Q. alien. Ecological niche overlap between two oak species was the widest in terms of the light treatment factor applied,and narrowest in terms of moisture. This response pattern was also verified by cluster and principle component analysis. These results suggest competitive interactions between Q. serrata and Q. aliena seedlings may be higher for light resources than moisture or nutrient resources, and that Q. serrata is more shade tolerant than Q. aliena.
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마비쪽 안쪽세로활 가동성 증진 운동이 뇌졸중 환자의 균형과 보행, 근활성도에 미치는 영향 : 증례 보고
이승혁,안광빈,전혜주 대한신경치료학회 2022 신경치료 Vol.26 No.3
Purpose The aim of this study was to investigate the effects of medial longitudinal arch mobility of paretic foot on balance and gait, and muscle activity in stroke patients. Methods Twelve stroke patients who were hospitalized at B hospital in Gyeonggido during the period from January 2022 to February 2022 were enrolled in this study. The subjects were divided into the medial longitudinal arch mobility training group of the paretic foot (n = 6) and the conventional physical therapy group (n = 6). The intervention was performed for 30 minutes a days, 5 times a weeks, and two weeks. The effectiveness of the intervention was assessed pre and postevaluated using the 10M Walk Test(10MWT), Berg Balance Scale(BBS), the BioRescue Platform(BRP) and the surface ElectroMyoGraphy(sEMG). Results As the result of the medial longitudinal arch mobility training on the paretic foot showed significantly improved balance and gait after exercise than before exercise in 10MWT, BBS and BRP. Conclusion Medial longitudinal arch mobility training of the paretic foot was effective in improving balance and gait speed through weightbearing on the paretic side in hemiplegic patients with stroke.
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