• 설비공학논문집
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• 제19권4호
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• pp.333-338
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• 2007

The object of this study is to find the optimal insulation design conditions of a HTS power cable cryostat. The optimum condition of a cable cryostat is obtained by varying types of MLIs, cable core weights, spacer diameters, winding pitches and MLI layer numbers. As the weight of cable core is increased, conduction heat transfer from surroundings to cable cryostat is increased. But as the spacer pitch is increased from 120 mm to 200 mm, the heat leak of cable cryostat remains almost constant. The optimal number of MLI layers is suggested. Double ply MLI is more effective than triple ply MLI and the insulation effect is best when the number of MLI layers is 36.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1995년도 추계학술대회 논문집
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• pp.183-186
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• 1995

The fabrication of dielectric multilayer mirror(DMM) optimized at the wavelength of 1.55$\mu\textrm{m}$ and its spectral properties were investigated. The materials used in the fabrication of DMM are TiO$_2$-SiO$_2$, which have the advantage of yielding high reflectance for relatively small numbers of layers. The optical constants of TiO$_2$single film were obtained by using a modified envelope method. The reflectances of DMMs with 3,7,11 and 23 layers were 58%, 89%, 97% and 99.9% at the wavelength of 1.55$\mu\textrm{m}$, respectively.

• 한국환경생태학회지
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• 제24권6호
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• pp.638-647
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• 2010

현존식생이 매토종자집단의 종조성에 미치는 영향을 알아보기 위해 소나무군락과 신갈나무군락의 식생구조를 분석하고, 표토를 채취하여 영남대학교 조경학과 유리온실로 옮긴 후 매토종자를 스티로폼 상자에 넣어 발아실험을 통해 매토종자 집단의 종조성과 개체수를 조사하였다. 표토를 채취한 두 군락의 자생지에서 층위별, 군락별 및 수종별로 매토종자집단의 종조성 및 개체수에 미치는 영향을 분석한 결과, 매토종자에서 두 군락의 초본층에 출현한 식물종이 교목층과 아교목층, 관목층의 식물종보다 유의적으로 높게 출현하였다. 두 군락 간 매토종자의 종수와 개체수는 유의적 차이가 없었다. 또한, 현존식생과 매토종자에 공통으로 출현한 식물종수는 두 군락 간 유의적 차이가 없었다. 매토종자에서 발아한 두 군락의 목본종은 천이중간 또는 후기의 수종보다 선구종 또는 주연부 수종의 발아율이 높았다. 따라서, 군락의 초본층 식물종이 매토종자집단의 종조성에 가장 크게 영향을 미치고, 우리나라의 동일한 삼림대와 위도를 고려한 군락별 매토종자집단의 종조성에는 큰 차이가 없는 것으로 보인다. 또한, 현존식생의 선구종 또는 주연부 수종이 매토종자로서 표토에 축적될 가능성이 높고, 이 수종이 매토종자집단의 종조성에 영향을 미치는 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.395-410
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• 2006

This paper reports the result of an investigation into wave propagation in orthotropic laminated piezoelectric cylindrical shells in hydrothermal environment. A dynamic model of laminated piezoelectric cylindrical shell is derived based on Cooper-Naghdi shell theory considering the effects of transverse shear and rotary inertia. The wave characteristics curves are obtained by solving an eigenvalue problem. The effects of layer numbers, thickness of piezoelectric layers, thermal loads and humid loads on the wave characteristics curves are discussed through numerical results. The solving method presented in the paper is validated by the solution of a classical elastic shell non-containing the effects of transverse shear and rotary inertia. The new features of the wave propagation in laminated piezoelectric cylindrical shells with various laminated material, layer numbers and thickness in hydrothermal environment and some meaningful and interesting results in this paper are helpful for the application and the design of the ultrasonic inspection techniques and structural health monitoring.

• Structural Engineering and Mechanics
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• 제14권6호
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• pp.661-677
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• 2002

The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.104-109
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• 2000

The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

• 한국측량학회지
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• 제26권3호
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• pp.275-284
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• 2008

수치지도의 효율적 갱신방안이 필요한 이유는 수치지도가 지자체 및 여러 지리정보시스템의 기본도로 활용되고 있어 수치지도의 수정갱신 이슈가 공간정보 활용 극대화의 열쇠가 되기 때문이다. 이에 본 연구에서는 수치지도의 건물레이어를 중심으로 그 속성정보를 효율적으로 갱신하기 위해 건축물대장과 연계하는 방안을 제시하였다. 이를 위해 가장 필수적인 사항은 두 자료의 건물간 연계가 일대일로 이루어져야 한다는 점으로, 본 연구에서는 건축물대장과 수치지도의 건물도형에 새주소사업의 건물번호를 공통으로 부여하여 일대일로 연계함으로서 ID 기반의 건물레이어 속성정보의 수정갱신 모델을 수립하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제30권2호
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• pp.275-283
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• 2017

Objective: An experiment was conducted to investigate the environment of the deep litter system and provided theoretical basis for production. Methods: The bedding samples were obtained from a pig breeding farm and series measurements associated with gases concentrations and the bacterial diversity as well as the quantity of Escherichia coli, Lactobacilli, Methanogens were performed in this paper. Results: The concentrations of $CO_2$, $CH_4$, and $NH_3$ in the deep litter system increased with the increasing of depth while the $N_2O$ concentrations increased fiercely from the 0 cm to the -10 cm depth but then decreased beneath the -10 cm depth. Meanwhile, the Shannon index, the dominance index as well as the evenness index at the -20 cm layer was significantly different from the other layers (p<0.05). On the other hand, the quantity of Escherichia coli reached the highest value at the surface beddings and there was a significant drop at the -20 cm layer with the increasing depth. The Lactobacilli numbers increased with the depth from 0 cm to -15 cm and then decreased significantly under the -20 cm depth. The expression of Methanogens reached its largest value at the depth of -35 cm. Conclusion: The upper layers (0 cm to -5 cm) of this system were aerobic, the middle layers (-10 cm to -20 cm) were micro-aerobic, while that the bottom layers (below -20 cm depth) were anaerobic. In addition, from a standpoint of increasing the nitrification pathway and inhibiting the denitrification pathway, it should be advised that the deep litter system should be kept aerobic.

• 태양에너지
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• 제8권1호
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• pp.33-40
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• 1988

The characteristics of thermal instabilities of natural convection in a horizontal fluid layer bounded below by a rigid plate and above by an interface with a passive gas is presented. The critical Grashof number decreases as the surface tension gradient effect (Marangoni effect) at the interface increases and the flow remains unstable for a critical Marangoni number depending on Prandtl numbers. These results are in substantial agreement with those of Smith and Davis.

• 미생물학회지
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• 제21권2호
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• pp.71-78
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• 1983

The number of aerobic free-living nitrogen fixation bacteria and factors in soil at different stands covered with Pinus rigida, Quercus acutissima and Zoysia japonica in Cheongju area were investigated from Feb. to Sept 1981. 1. The numbers of $N_2-fixation$ bacteria, according to the seasonal changes, increased gradually from winter to spring and summer. But the growth pattern revealed some differences in accordance with plant cover stands : the numbers increased abruptly in May at Pinus, May-June at Quercus and Apr. May at Zoysia stand. The pick of numbers represented in Aug. Sept, at Pinus, Jul-Aug. at Quercus and May-Jun. at Zoysia stand, respectively. 2. The interrelationship between the monthly changes of enviotnmental factors and numbers of $N_2-fixation$ bacteria at different stands, mainly depends upon the soil temperature than other soil factors (r=0.71-0.84). The numbers of $N_2-fixation$ bacteria may increase 5-7 times according to increase $10^{\circ}C$ of soil temperature, and optimal range was $20{\sim}30^{\circ}C$ for growth. Equation of the interrelation between soil temperature and numbers could be stated as follows : log y=ax+b. 3. In the case of high soil temperature, the bacterial numbers presented high level in drought periods. Therefore, the $N_2-fixation$ bacterial species in these soil seem to consist of resistant to desication. 4. The influence of soil organic matter for growth of $N_2-fixation$ bacteria indicated low conrelation. The reason may seen the content of organic matter in these soil existed abundantly above the quantities of limitation for growth. 5. In artifical gradients, the $N_2-fixation$ bacteria were predominated at $20{\sim}30^{\circ}C$ same as natural condition, pH7-8, and 20-30% of soil water contents. 6. The vertical distribution of bacteria marked decreasing trends from surface to lower layers, and the decreasing degree was shown well in Zoysia, Quercus and Pinus stand in order. But in the trees, the numbers increased at 30cm layer estimated the region of root than 20cm layer. 7. Both catalase megative and positive group of $N_2-fixation$ bacteria in soil increased according to the rise of the soil temperature. Catalase positive group was revealed as dominant group in winter, and catalase negative group revealed in summer. The change of dominant pattern was shown during Feb. to Apr.