• Journal of The Korean Society of Grassland and Forage Science
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• v.12 no.3
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• pp.48-55
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• 1992

자연초원(natural grassland)은 연간 강수량이 $250\sim1000mm$, 기온이 $0\sim26^{\circ}C$인 지역에서 형성되는 기후극상의 식생으로써 초본식물, 특히 벼과식물이 우점되어 있다. 이 자연초원은 세계에 널리 분포되어 있는데 지역에 따라 온대초원 열대초원, steppe, prairie, pampa등으로, 식물의 초고에 따라 장초형 초원 단초형초원으로 분류한다. 한국에는 연간 강수량이 많고 연평균기온이 높아서 기후 극상의 자연초원은 성립되지 못하고 식생천이의 도중상으로 소규모의 초본식물군락이 나타난다. 이들은 주로 방치된 경작지나 경작지주변의 인간간섭이 많은곳, 해수나 강물의 영향으로 나무가 생장할 수 없는 곳에 식생천이의 도중상으로 나타나거나, 산림이 산불이나 벌목으로 파괴된 곳에서 제2차천이의 과정으로 초본식물군락이 출현하는데 이것을 야초지(native grassland)라고 한다. 특히 야초지에 가축을 사육할 목적으로 목초를 재배하여 이용할 때는 초지라고 한다. 한국의 야초지식생을 구성하는 주요 우점초종은 억새, 새, 솔새, 잔디, 갈대, 쑥 등이며 건조하고 기온이 높은 여름에는 C-4형 식물이, 수분이 많고 서늘한 봄과 가을에는 C-3형 식물이 높은 생산성을 나타낸다. 야초지는 지표면을 피복하여 바람이나 빗물에 의한 토양침식을 방지할 뿐만아니라 초식동물의 먹이를 생산하고 자연경관을 아름답게 가꾸어 주는 중요한 역활을 하고 있으나 공장부지 주택지 농업용지등으로 개발되어 없어지고 관리가 이루어지지 않아 황폐화 되고 있다. 야초지를 효과적으로 보전하고 이용하기 위해서는 생장이 빠르고 생산성이 높은 우수한 목초를 재배하는 것이 바람직한데 그 방법으로는 겉뿌림초지조성법, 제경법, 시비법이 이용된다.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.53-62
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• 2014

In Korea, in general, separation distance between existing parallel tunnels was set at two to five times as distant as the diameter of the tunnels according to ground conditions. Recently, however, actual applicability of closely spaced parallel tunnels whose distance between tunnel centers was shorter than the diameter has increased due to environmental damages resulting from massive cutting, restriction in purchase of required land, and maintenance of linear continuity. In particular, when the pillar width of tunnel decreases, the safety of pillars affects behaviors of the tunnel and therefore the need for diverse relevant studies has emerged. However, research so far has been largely confined to analysis of behavior characteristics of pillars, or parameters affecting design, and actually applicable and quantitative data have not been presented. Accordingly, in order to present a stability evaluation method which may maximally reflect construction conditions of spots, this study reflected topographical and stratigraphic characteristics of the portal part with the highest closeness between the tunnels, simulated multi-layer conditions with rock mass and complete weathering, and assessed the degree of effect the stability of pillars had on the entire tunnels through numerical analysis according to changes in pillar width by ground strength. This study also presented composite analysis result on ground surface settlement rates, interference volume rates, and average strength to stress and a formula, which may be applicable to actual work, to evaluate safety rates of closely spaced parallel tunnel pillars and minimum pillar width by ground strength based on failure criteria by Hoek-Brown (1980).

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.618-629
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• 2001

This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied by establishing an effective root cause failure analysis. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal cycling test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which might cause electrical short in underlying circuitry, can occur during curing or thermal cycle. The results can be conveniently used to quickly identify defective lots, determine $B_{10}$ life estimation each lot at the level of inspection, and detect major changes in the vendors processes. Also, the condition for dielectric breakdown was investigated for the estimation of failure rate with load-strength interference model.

• Journal of The Geomorphological Association of Korea
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• v.17 no.1
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• pp.39-48
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• 2010

This is a case study to research the environmental changes that occurred during the Latter Half of the postglacial age around the Basin of Onyang River in Asan, Korea. In line with this purpose, the author performed a pollen analysis and a radiocarbon dating on the deposits of alluvial fan around the upper Geumgok River, a tributary of Onyang River. Sampling point was at the altitude of about 67.5 meters, which belongs to the central zone of the cool temperate forest. The followings are the results of the study. The study area has passed through SC-I (the coniferous forest period in which Pinus was dominant), SC-II (the deciduous broad-leaved forest period in which Quercus and Castanea were dominant) and SC-III (the mixed conifer and deciduous broad-leaved forest period, in which Pinus, Quercus and Ulmus/Zelkova were dominant) respectively since about 3,000 yrB.P. SC-I period and SC-II period are presumed to be between about 3,000 and 2,000 yrB. P., and SC-III period to begin after 2,000 yrB.P. In comparison with the nationwide pollen zone during the postglacial age, SC-I and SC-II periods are contrasted with the R-IIIa zone and also the SC-III zone with the RIIIb zone. In addition, it is assumed that Pinus densiflora forest luxuriated there since 2,000 yrB.P. due to the destruction of forests, and that a lot of Fagopyrum pollen appeared; altogether, it was the so-called human interference period, from which forests began to be markedly destroyed. It is concluded that in those days inhabitants leaded agricultural life.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.53-62
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• 1992

Material can be degraded by using it for a long service under the high temperature and pressure circumstances, Therefore, material degradation can affect the strength of mechanical structures. At present, the life prediction of the degraded structures is considered as an important technical problem. In this paper, the degraded 21/4Cr-lMo steel is the material used for about 10 years around 400.deg. C in an oil refinery plant. The recovered one was prepared out of the above degraded steel by heat treatment for one hour at 650.deg. C. The degradation effect was investigated through the tension test, Hardness test and Charpy impact test. On the smooth surface material, the fatigue crack initiation, growth and coalescence stages of the distributed small cracks were investigated with photographs, and the crack length and density were measured. The measuring results were analyzed by quantative and statistical methods.

• The Korean Journal of Quaternary Research
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• v.13 no.1
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• pp.1-23
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• 1999

A palynological investigation of the Annyeong-ri, Hwasung-gun Gyeonggi-do, in where Yung-Nung and Gun-Nung are located, was carried out for the first time. From the pollen analysis, two pollen zones are established: Pollen Zone I : Ainus-Quercus-Pinus and Pollen Zone Ⅱ : Pinus. Pollen Zone I is characterized by Mixed coniferous and deciduous broadleaved vegetation during about 3,500 yr. B.P.-2,000 yr. B.P., while after 2,000 yr. B.P. Pollen Zone Ⅱ appears to be Coniferous vegetation and Evergreen broadleaved vegetation. The former reflects there was a lowland fluvio-lacustrine environment before fully lacustrine one which represents the latter. Pollen analysis indicates the vegetation before 2,000 yr. B.P. was controled by environmental factor such as climate conditions, whereas after that time vegetation was strongly effected by human's impact. It is concluded that pollen analysis is useful to find out the relationship between vegetation history and man's interference. In addition freshwater algae play to tell the lake environments.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.387-401
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• 2007

Recently, because of the restriction of land for construction and interference of adjacent structure, parallel tunnels with small clearance have been planned and constructed in many sites. In this case, the stability of pillar at center part is very important factor to satisfy the stability of tunnel structure under the construction. In this paper, numerical analyses for the asymmetry parallel tunnels with a narrow width of pillar have been carried out to search for the optimum reinforcement measure for rock pillar and verify the stability of tunnel. Rock pillar between each single tunnel is supposed to be under heavy load by rock mass. The analysis of stress state at rock pillar at various cases for construction conditions is required to investigate the structural behaviour of tunnels and stability of the pillar. Strength-stress ratio is calculated based on the failure theory of rock and the safety factor of tunnel is computed with strength reduction technique. Through these numerical results, reasonable reinforcement measures for rock pillar at parallel tunnel were established and recommended.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3048-3057
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• 1996

Analysis model containing two inclined surface cracks on semi-infinite elastic body is established and analyzed on the basis of linear fracture mechanics to examine mutual interference of two surface cracks. Muskhelishvili's complex stress functions are introduced and a set of singular integral equations is obtained for a dislocation density function. The stress intensity factors at crack tip are obtained by using the Gerasoulis'method. When two surface cracks are parallel and have the same length, the values of $K_1$and $\Delta K_11$(variation of $K_11$) for crack 1 and crack 2 decrease by the mutual interference of two surface cracks as the distance between the two surface cracks shortens. The effect of mutual interference is remarkable in high friction coefficient. In case that two surface cracks are parallel, the values of $K_1$and $\Delta K_11$for crack 2 decrease as the length ratio ot crack 2 to crack 1 becomes small. As the crack inclination angle rises, the value of $K_1$ and the mutual interference of $K_1$for crack 2 increase and the value of$\Delta K_11$ for crack 1 becomes smaller than that for crack 2.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.369-372
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• 2003

This paper describes a design of OFDM (Orthogoanl Frequency Division Multiplexing) based wireless LAN system receiver, defined in IEEE 802.11a standards. Because OFDM system uses several orthogonal sequence sets, it ran avoid selective fading of fast data transfer problem when it is used with error correction code. But if the receiver is not synchronized, the orthogonal of between sub-ralliers will be destroyed and the data interruption will be generated. So it makes error property get worse very murk. For improving the noise error, we use the relationship of phasor between sub-carriers and make system synchronization using one tab equalizer. The designed OFDM block is described by Verilog HDL for the efficient and small size hardware. And we preform the functional verification and evaluation using the vector of standards.

• Korean Journal of Environmental Biology
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• v.25 no.3
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• pp.215-222
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• 2007

DMZ (De-Militalized Zone) in South Korea is world heritage area by passage control of human-being for more than 50 years since 1953. Wild flora and fauna in these area have been protected from any development and/or habitat destruction. However, consideration on ecosystem and nature in the area is becoming higher, and demand for development is raising also. We have reviewed any publications, which are surveyed about ecosystem and interview local residents about wildlife inherit there. Totally 51 species have been reported inhabited DMZ belonging to 17 Families, 6 Orders, so far. National monuments in DMZ are following; Asiatic black bear (Ursus thibetanus), Eurasian otter (Lutra lutra), Musk deer (Moschus moschiferus), KOREAN goral (Nemorhaedus caudatus), flying squirrel (Pteromys volans) and spotted seal (Phoca vitalima). These results would be an essential data to establish management strategy and manuals for conserving native ecosystem, native flora and fauna in DMZ, and also using for registering world heritage area under UNESCO.