• 한국정밀공학회지
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• 제27권10호
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• pp.45-51
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• 2010

Electrical discharge drilling (ED-drilling) is a widespread machining method used to bore small holes with a high aspect ratio. This paper presents additional methods by which ED-drilling can improve machining speed, tool wear, and machined surface quality. Firstly, for high machining speed, and low tool wear, a new-type electrode that was ground on one side or both sides of the cylindrical electrodes was suggested to expel debris. The debris which is generated during the machining process can cause sludge deposition and secondary discharge problems: major reasons to decrease machining speed. This new-type electrode also reduced tool wear that was due to the decrease of unstable discharge in a machining gap by helping to expel waste water and debris from the gap. Secondly, to improve the machined surface roughness, an electrolyzation process was included after drilling. This process made the machined surface smooth by means of an electrochemical reaction between an electrode and a workpiece. In this study, the machining speed, electrode wear, and surface roughness were improved by the newtype electrode and the electrolytic process.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1285-1289
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• 2006

In a large diameter piping system, high frequency energy can produce excessive noise, high vibration, and failures of thermo-well, instrumentation, and attached small-bore piping. High frequency energy is generated by flow induced vibration like vortex shedding in orifices and valves. Once this energy is generated, amplification may occur from acoustical and/or structural resonances, resulting in high amplitude vibration and noise. At low frequencies, pipe vibration occurs laterally along the pipe's length, but at higher frequencies, the pipe shell wall vibrates radially across its cross-section. The simple beam analogy which is based on the beam mode vibration can not be applied to evaluate shell mode vibration. ASME OM3 recommends that the stress be measured directly by strain gauge and be evaluated according to the fatigue curves of the piping material. This Paper discusses the excitation and amplification mechanism relevant to high frequency energy generation in piping system, the monitoring method of the shell mode vibration in ASME OM3, the evaluation method generally used in the industry. Finally this paper presents the stress evaluation of the cavitating venturi down stream piping, where high frequency shell mode vibrations were observed during the operation.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2552-2564
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• 2020

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neigh-bouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.

• Journal of Electrical Engineering and information Science
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• 제2권6호
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• pp.95-105
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• 1997

In this paper, we have studied about design and fabrication of the actively shielded superconducting MRI magnet. Nonlinear optimization methods are usually used to find optimum coil configurations. However the selection of initial coil configurations is very difficult. In case bad initial data are used, it is even impossible to find optimum coil configurations which satisfy predefined constraints. We have developed computer optimization program which consists of two steps. Initial coil configurations are easily selected through linear optimization in the first step and optimum coil configurations are found through nonlinear optimization in the second step. We have also studied about superconducting shim coils to cancel error fields caused by coil fabrication errors. Many researchers published design concepts of shim coil. However all these studies are for shim coil design using filamentary coils with single turn, Shim coils with multi-turns should be used to produce enough field strength to cancel error fields. We have developed computer program for the design of shim coils which have proper thickness and length. An actively shielded superconducting MRI magnet with a small warm bore was fabricated and four sets of superconducting shim coils were equipped. The magnetic field distributions were measured and field correction was carried out using shim coils.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 춘계학술대회
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• pp.86-93
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• 1996

The lubrication characteristics of high-speed ball bearings has been investigated empirically using 45mm bore split inner ring ball bearings employed in small industrial gas turbine engines with oil-jet lubrication method. For the close structural simulation, experiments carried out with bearing mounting supports of real engines, such as bearing housings and oil nozzle assemblies with squeeze film dampers. Thus the results of tests can be directly applied to the design and the development of gas turbine engines. Testing was done by varying operating speeds, axial load on bearings, and lubricant flowrates. During testing, the temperature of bearing at outer-ring face, the power consumption of the driving motor, and the rotating resistance of the bearing were measured. From this study, the representative factors for lubrication characteristics at high speed was found, and the most important one was not operating speed but axial load up to 1.95 million dmN speed and 303 kgf axial load. Furthermore, the detailed variation of the rotational resistance of the bearing could be visualized by measuring the change of the radial load under the bearing supports. The rotational resistance consists of the frictional resistance and the bearing-cavity oil resistance.

• 한국환경농학회지
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• 제38권2호
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• pp.89-95
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• 2019

BACKGROUND: Liquid pig manure (LPM) has been used as an alternative for conventional fertilizers on some gramineous crops. However, its chemical properties varied widely depending on the degree of the digestion. A pot experiment was conducted to determine the responses of persimmon trees to immature (not well-digested) LPM application. METHODS AND RESULTS: Ten application levels of immature LPM, consisted of a total of 3 to 30 L in 3-L increment, were applied during summer to 5-year-old 'Fuyu' trees grown in 50-L pots. Increasing the LPM application rate caused defoliation, wilting, and chlorosis in leaves. When applied with the rate of 3 L during summer, the tree produced small fruits with low soluble solids and bore few flower buds the following season, indicating insufficient nutritional status. In trees applied with the LPM rates of 6~12 L, both fruit characteristics and above-ground growth of the trees appeared normal but some roots were injured. However, application of higher LPM rates than 27 L resulted in small size, poor coloration, or flesh softening of the fruits the current season. Furthermore, the high LPM rates caused severe cold injury in shoots during winter and weak shoot growth the following season. It was noted that the application of higher LPM rate than 9 L damaged the root, even though above-ground parts of the tree appeared to grow normally. CONCLUSION: The results indicated that an excessive immature LPM application could cause various injuries on leaves, fruits, and the roots in both the current and the following season.

• 식물분류학회지
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• 제52권4호
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• pp.226-234
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• 2022

The study aims are to examine the characteristics of artificial and natural hybrids between Viola albida var. albida (= albida, from below) and V. albida var. chaerophylloides (= chaerophylloides, from below), and to confirm if hybrids could be fertile and make populations in their native habitats. The 1st filial (= F₁, from below) leaf shape produced by artificial crossing between albida and chaerophylloides was the same as that of V. albida var. takahashii (= takahashii, from below), and F₁ bore also both chasmogamous and cleistogamous flowers. F₁ seed number was 9.6 per cleistogamous pods, which was remarkably less than the average of 38.2 for albida and chaerophylloides, but the germination rate was all similar. The leaf type of self-crossed 2nd offsprings (= F₂, from below) showed all leaf types found in the Viola albida complex, but the ratio of chaerophylloides leaf type was relatively low. Individuals whose F₂ leaf type was restored to albida produced an average of 31.4 seeds per capsule, meaning that fertility was restored. On the other hand, individuals of F₂ takahashii leaf type come to fruition a low average of 10.4 seeds per capsule, which is similar to that of takahashii. The results of crossbreeding experiment, where is their native habitats, were similar to that of laboratory. Both albida and chaerophylloids in Mt. Bulmyeong distribute extensively, but takahashii make a small population only in places where albida and chaerophylloides grow together. Summarizing the above results is suggesting that the speciation of takahashii was done by hybrid between albida and chaerophylloides, and these have been maintained with relatively small population by cleistogamous capsules.

• 한국수산과학회지
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• 제14권3호
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• pp.165-170
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• 1981

우리나라 미역양식의 발상지인 동해남부연안의 미역양식장에서 세균성이라고 생각되는 미역녹반증과징소갑각류의 기생에 연한 바늘구멍증, 미역 속구멍증 등의 병충해와 계장홍조류인 플리시포니아의 착생에 인한 피해를 확인할 수 있었다. 1. 김 녹반증과 유사한 녹색의 반점이 미역엽상체의 하반부에 나타나서 점차 확대되면서 반점의 조직이 붕괴하여 녹색의 테두리를 가진 구멍이 엽면에 생긴다. 엽상체 끝 부분의 구명은 더욱 확대 유합하여 끝 녹음을 조장하는 결과가 된다. 이 병증은 동일양식장에서도 중심부일수록 피해가심하고 주녹부, 특히 외해쪽은 피해가 적었다. 이 병증이 있는 엽체는 외관상 건전한 엽체보다 $70\sim100$배 더 세균에 오탁되어 있었으며 병증이 있는 엽체에서 분리된 세균중에서 다음 여에 속하는 균주가 많았다. Moraxella, Acromobacter, Vibrio, Flavobacterium, Acinetobacter, Pseudomonas. 2. 엽체에 1열로 동일간격으로 $5\sim10$개의 미세한 바늘구멍을 여기 저기에 볼 수 있었고 이들 바늘구멍이 다소 불규칙하게 모여 있는 것도 희구했다. 이것은 요각류인 Harpacticoid의 1종인 Thalestris sp.의 기생에 의한 것이다. 이 기생이 발견되었던 초기는 3월경에 나타났었으나 점차 출현시기가 앞당겨져서 지금은 전등의 12월부터 출현한다. 3. 단각류의 1종인 미역속별레, Ceinina japonica Stephesen이 중륵에 기생하여 엽상체 유실의 원인도 되고 심한 것은 중륵에서 종으로 엽상체가 2분되는 것도 있었다. 이것은 양식말기에 주로 나타난다. 4. 조간대 암상에 생육하는 폴리시포니아 Polysiphonia spp.가 종연와 함께 씨줄에 다수 착생하였다가 양식장에서 미역 유아와 경합을 하여 미역 착생면을 차지하여 피해를 준다. 끝으로 본 조사는 1980등도 문교부연구조성비로 수행되었으며, 세균을 분리동정해 주신 장동석 교수와그의 교실원에 감사한다.

• 한국응용곤충학회지
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• 제23권4호
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• pp.233-236
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• 1984

본 연구는 경상남도 진주에 위치한 농촌진흥원 해충 시험포장에서 Carbofuran 입제를 본답기에 2회 처리와 농가 관행방제인 살충제 9회 처리간의 벼 해충과 이들 천적의 밀도를 비교 조사하였다. 1. Carbofuran $3\%$ 입제를 기계이앙시 육묘상자 처리와 7월중순 수면 처리등 본답기에 2회만 처리하여도 벼의 주요해충인 멸구 매미충류, 나방류, 굴파리, 총채벌레등의 방제효과가 관행 방제인 살충제 9회 처리와 비등한 경향이었다. 2. 벼 해충의 천적인 거미류와 멸구류의 난기생봉(Anagrus sp.)의 밀도는 Carbofuran 입제 처리가 관행방제보다 2.4배 밀도가 높았다.

• Parasites, Hosts and Diseases
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• 제41권1호
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• pp.17-25
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• 2003

The tegumental ultrastructure of juvenile and adult Himasthla alincia (Digenea: Echinostomatidae) was observed by scanning electron microscopy. One-, 5- (juveniles) and 20-day-old worms (adults) were harvested from chicks experimentally fed metacercariae from a bivalve, Mactra veneriformis. The juvenile worms were elongated and cu wed ventrally. The head crown bore 31 collar spines, arranged in a single row. The lip of the oral sucker had 12 paired, and 3 single type 1 sensory papillae, and the ventral sucker had about 25 type II sensory papillae. The anterolateral surface between the two suckers was densely packed with tegumental spines with 4-7 pointed tips. The adult worms were more elongated and filamentous, and had severe transverse folds over the whole body surface. On the head crown and two suckers, type 1 and 11 sensory papillae were more densely distributed than in the juvenile worms. Retractile brush-like spines, with 8-10 digits, were seen on the anterolateral surface, whereas claw-shaped spines, with 2-5 digits, were sparsely distributed posteriorly to the ventral sucker The cirrus characteristically protruded out, and was armed with small spines distally. The surface ultrastructure of H. alincia was shown to be unique among echinostomes, especially in the digitation of its tegumental spines, the distribution of sensory papillae and by severe folds of the tegument.