• 한국정밀공학회지
• /
• 제1권2호
• /
• pp.47-57
• /
• 1984

The porous matterials are used both to control the flow of the compressed gas and to serve as the bearing surface. This porous design offers several advantages over the conventional externally pressurized gas bearings. It can simplify the construction, lower the gas consumption, and make the cleaning of the gas supply less critical. Test apparatus was cinstructed to experi- mentally investigate maximum load capacity of thrust bearing was measured 200 Kg (15Kg/$\mu$m), and radial bearing was 36 Kg/$\mu$m. And a rotation accuracy of face waving was 0.0127$\mu$m, and center waving was measured 0.5 $\mu$m. Finally, the use of this method of design and manufacturing will contribute to many practical application in the field required for precision and high stability.

• 한국소음진동공학회논문집
• /
• 제19권4호
• /
• pp.393-399
• /
• 2009

Historically, industrial condition monitoring has been performed by costly hard-wired sensors or infrequent checks by maintenance personnel equipped with hand held monitoring equipment. Self- powered wireless condition monitoring systems provides on-line monitoring of critical plant and machinery providing major operating cost benefits. A vibration energy harvester(VEH) is a device that converts kinetic energy occurred by machine vibration into useable electrical energy. Using VEHs to power wireless monitoring systems can yield significant benefits: increased reliability, lower life time costs and no battery disposal issues, etc. This paper proposes the novel prototype design and manufacturing of a VEH that can eliminate the effect by failed batteries.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2008년도 춘계학술대회 논문집
• /
• pp.305-308
• /
• 2008

This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a grounding rod. Soil ionization phenomena are investigated by using both voltage and current signals recorded by oscilloscope. As a result, a critical electric field intensity($E_C$) for ionization is decreased with reduction of grain size. The pre-ionization resistance($R_1$) and post-ionization resistance($R_2$) at the sand with fine grain size are getting lower with increasing current magnitude. Finally, the time to ionization($t_1$) and ionization current peak($t_2$) of fine grain size are significantly shorter than those of medium grain size.

• 한국연초학회지
• /
• 제8권1호
• /
• pp.57-67
• /
• 1986

This study was conducted to find out the effects of chlorine on the yield, chemical constituents and physical properties of Burley leaf tobacco. The results obtained are as follows. 1. There was no significant differences in growth and yield among chlorine application levels. 2. When chlorine being applied 4kg/10a or more, the cured leaf showed higher chlorine content and lower leaf quality remarkably. It was estimated that the critical application of chlorine was 3kg/10a. 3. Total nitrogen and alkaloid contents of cured leaf were increased by chlorine application, while the phosphorus, calcium and magnesium were not affected. 4. The reflectance color of red and yellow were decreased by cvhlorine application in cured leaf of field grown tobacco.

• Smart Structures and Systems
• /
• 제19권2호
• /
• pp.163-179
• /
• 2017

The axisymmetric buckling delamination of the Piezoelectric/Metal/Piezoelectric (PZT/Metal/PZT) sandwich circular plate with interface penny-shaped cracks is investigated. The case is considered where open-circuit conditions with respect to the electrical displacement on the upper and lower surfaces, and short-circuit conditions with respect to the electrical potential on the lateral surface of the face layers are satisfied. It is assumed that the edge surfaces of the cracks have an infinitesimal rotationally symmetric initial imperfection and the development of this imperfection with rotationally symmetric compressive forces acting on the lateral surface of the plate is studied by employing the exact geometrically non-linear field equations and relations of electro-elasticity for piezoelectric materials. The sought values are presented in the power series form with respect to the small parameter which characterizes the degree of the initial imperfection. The zeroth and first approximations are used for investigation of stability loss and buckling delamination problems. It is established that the equations and relations related to the first approximation coincide with the corresponding ones of the three-dimensional linearized theory of stability of electro-elasticity for piezoelectric materials. The quantities related to the zeroth approximation are determined analytically, however the quantities related to the first approximation are determined numerically by employing Finite Element Method (FEM). Numerical results on the critical radial stresses acting in the layers of the plate are presented and discussed. In particular, it is established that the piezoelectricity of the face layer material causes an increase (a decrease) in the values of the critical compressive stress acting in the face (core) layer.

• Progress in Superconductivity
• /
• 제14권1호
• /
• pp.30-33
• /
• 2012

We have grown $MgB_2$ superconducting thin films on the SiC buffer layers by means of hybrid physical-chemical vapor deposition (HPCVD) technique. Prior to that, SiC was first deposited on $Al_2O_3$ substrates at various temperatures from room temperature to $600^{\circ}C$ by using the pulsed laser deposition (PLD) method in a vacuum atmosphere of ${\sim}10^{-6}$ Torr pressure. All samples showed a high transition temperature of ~40 K. The grain boundaries of $MgB_2$ samples with SiC layer are greater in amount, compare to that of the pure $MgB_2$ samples. $MgB_2$ with SiC buffer layer samples show interesting change in the critical current density ($J_c$) values. Generally, at both 5 K and 20 K measurements, at lower magnetic field, all $MgB_2$ films deposited on SiC buffer layers have low $J_c$ values, but when they reach higher magnetic fields of nearly 3.5 Tesla, $J_c$ values are enhanced. $MgB_2$ film with SiC grown at $600^{\circ}C$ has the highest $J_c$ enhancement at higher magnetic fields, while all SiC buffer layer samples exhibit higher $J_c$ values than that of the pure $MgB_2$ films. A change in the grain boundary morphologies of $MgB_2$ films due to SiC buffer layer seems to be responsible for $J_c$ enhancements at high magnetic fields.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
• /
• pp.189-195
• /
• 1999

We have studied the vortex dynamics in YBa$_2Cu_3O_7$ single crystals with columnar defects using micro Hall-probe array. The Hall-probe array technique allowed a simultaneous measurement of the time and spatial dependence of the vortex density so that more detailed information on flux dynamics could be obtained. We found that field profiles inside sample were similar to the Bean's critical state model from the magnetic hysteresis measurement. Normalized relaxation rates were maximum near the center and decreased toward the edge if applied field H$_{app}$ is greater than the penetration field H. But applied magnetic field H$_{app}$ is less than H, relaxation rates were minimum near the center and increased toward edge. We found that glassy exponent ${\mu}$ has the value of ${\sim}$ 1 whose corresponding vortex motion is half-loop excitation. However, single vortex creep, ${\mu}$ ${\sim}$ 1/7, was also found at 30 K and H$_{app}$ ${\cong}$ H'. Calculation of activation energy, U, was possible from direct analysis of the local relaxation data using the basic diffusion equation. From these results, we found that U increases logarithmically with time and U around center was lower than that at the edge.

• 상하수도학회지
• /
• 제30권1호
• /
• pp.19-31
• /
• 2016

The Saemangeum watershed is required to manage water pollution effectively but the effect of liquid manure (LM) on soil and water quality in the basin is not clearly identified as yet. This study aims at assessing the effect on soil of a rice field and water quality of water bodies near the rice field during rice-crop time period to find out the effect of LM, the effect of rainfall, and the effect of rice-crop environment on soil and water quality by analyzing data of nitrogen components. As a result of the LM distribution, $NO_3-N$ was much higher than other N components in the entire soil layers and it was accelerated by rainfall right after the LM distribution. Compared to chemical fertilizer (CF), LM was slightly affected but still influenced on the surface water quality. During weak rainfall, low nitrogen concentration in topsoil was resulted as NH3-N decreased and Org-N and $NO_3-N$ increased. $NO_3-N$ concentration in the water of irrigation canals increased with time. During intensive rainfall, $NO_3-N$ and Org-N of the soil were measured highly in the submerged condition, while the water quality of the rice field was lower due to flooding into the irrigation canal as well as the growth of the rice plants. Also, total nitrogen was increased more than 7 times and it showed serious water quality deterioration due to LM and excessive fertilizer distribution, and rainfall during all rice-crop processes. The effect of LM on water quality should be studied consistently to provide critical data while considering weather condition, cropping conditions, soil characteristics, and so on.

• 한국잠사곤충학회지
• /
• 제16권1호
• /
• pp.1-20
• /
• 1974

본 연구는 산지개간상전에 발생하는 발아불량현상의 원인을 구명하고 방제법을 대립코자 1971∼1974년까지 4개년간에 걸처 실시하였으며 그 결과는 다음과 같았다. 1. 피해증상은 춘기에는 지조의 선단부가 발아를 하지 않거나 발아도중 즉 탈포∼연구기까지 진행되다가 갑자기 말라 죽는다. 발아불량지조의 피층 및 인피부에는 Necrosis 현상이 일어나고 갈색으로 변한다. 추기에는 엽의 노화, 선단엽의 이상, 엽맥, 엽병이 양변한다. 2. 발아불량상전토양은 화강암모재에 점질의 비율이 매우 낮은 사양토로 되어 있으며 하층토가 치밀 견고하고 공극률이 너무 적어서 근군발달에 매우 불량한 토양구조로 되어 있었다. 특히 발아불량극심지의 심토는 건전지에 비하여 고상이 과대하여 한발시에는 수분부족현상이 일어나기 쉬운 조건을 갖추고 있었다. 3. 발아불량극심상전은 건전상전에 비하여 토양수분함량이 유의하게 적었으며 특히 심토의 수분함량은 건전지가 적당한 수분함량을 유지하고 있었는데 반하여 발아불량극심지는 거의 위조점에 가까운 수분함량이었다. 4. 유방토심은 발아불량상전이 건전상전에 비하여 얕았고, 발아불량정도가 기한곳일수록 유방토심은 얕아지는 경향을 나타냈다. 5. 토양수분함량의 경시적변화는 토양내 유방붕소함량에 영향을 미쳤으며 발아불량상전의 수분함량은 건전상전에 비하여 6월 5일부터 9월 5일까지 계속 적은 함량을 유지하고 있었고, 유방붕소함량도 수분함량의 증감과 같은 경향으로 변화되였다. 6. 토양의 pH(4.7-5.6)와 유방붕소함량간에는 상관관계가 없었으나 유기물함량과 유방붕소함량간에는 고도의 정상관관계가 있었다. 7. 토양중 유방붕소함량은 발아불량상전이 0.19∼0.28ppm, 건전상전이 0.34∼0.43ppm으로서 발아불량상전보다 유의하게 많았다. 8. 엽 및 피층내의 붕소함량은 발아불량수가 건전수보다 유의하게 적었다. 9. 사경시험의 붕소결제구에서는 발아불량현상이 유발되었으며 그 피해증상은 포장에서 발생되는 증상과 동일하였다. 10. 석회의 시용은 시용량이 증가할 수록 발아불량현상을 다소 높게하는 경향이 있었다. 이상의 결과를 종합하여 볼때 뽕나무의 발아불량현상은 붕소의 결핍에 기인되나 붕소의 결핍피해정도는 토양모재, 토양내 유기물함량 및 수분함량 그리고 석회시용등에 의해서도 좌우되는 것으로 인정된다. 11. 발아불량현상은 붕사를 10a 당 6∼9kg을 춘, 하2회분시하면 방제할 수 있으며, 10a당2,000kg의 퇴비를 수년간 계속시용하는 방법도 상당한 방제방과를 얻을 수 있다고 믿어진다.

• 한국자기학회지
• /
• 제8권1호
• /
• pp.34-41
• /
• 1998

본 연구에서는 비가역 자벽이동 및 결맞음회전 이론을 함께 고려하여 단순 일축 자성체의 돌림힘곡선에서는 둥근(미분가능한) 정점들이 존재하기 위한 조건을 구하고 돌림힘 곡선의 개형을 이론적으로 연구하였다. 일축 비등방성 자성체의 돌림힘 곡선을 인가 자기마당이 변화함에 따라, 이력현상의 유무 및 자기화 역전기구의 종류와 미분 가능한 정점의 갯수에 의해 8가지의 유형들로 구별할 수 있었다. 비등방성 자기마당 세기가 같은 시료라도 자벽의 생성 및 이동에 필요한 최저 임계자기마당 세기가 다르면 상이한 모양의 돌립힘 곡선을 보였다. 한편, 미분 가능한 정점의 높이를 활용하여 포화 자기화량 및 비등방성 에너지 상수를 측정하는 기존의 돌림힘 곡선 해석법들은 인가 자기마당 세기가 비등방성 자기마당 세기의 약 77% 이상일 때 정확한 측정이 가능함을 알 수 있었다.