• 공업화학
• /
• 제8권1호
• /
• pp.67-75
• /
• 1997

LLDPE와 미분말 상태인 강산성 양이온 교환 수지를 사용하여 압출기를 통해 막상으로 성형한 후 증류수와 NaCl 포화 수용액상에서 후처리하여 불균질 양이온 교환막을 제조하고 특성화하였다. 증류수 및 NaCl 포화 수용액 중에서 후처리를 통하여 양이온 교환 수지 입자가 함수, 팽윤되어 폴리에틸렌과 이온 교환 수지 사이에 cavity가 발생하며 동시에 양이온 교환 수지의 팽윤 압력에 의해 결합제에 큰 힘이 작용하기 때문에 폴리에틸렌에 micro-crack이 생성되므로 전기 화학적, 물리적 특성 값이 향상되었다. 또한 후처리 시간 30분과 후처리 온도 $90^{\circ}C$에서 최적의 조건을 갖는 우수한 불균질 양이온 교환막이 제조되었다.

• 한국터널공학회:학술대회논문집
• /
• 한국터널공학회 2005년도 학술발표회 논문집
• /
• pp.233-247
• /
• 2005

Most tunnel lining material which has been used in the domestic is a concrete. But many problems as the construction period, the cost, and the crack occurrence for the design, construction, and management were happened in the concrete lining. For this reason, many research institutes like the Korea Highway Corporation recognize the necessity of an alternate material development and grow on the interest for that. So in this study, the seismic behaviour characteristics for the application of the Corrugated Steel Plate Lining in cut-and-cover tunnel are evaluated as several conditions for the backfill height, the cutting slope, and the relative density of backfill soil are changed. The compressive stress which is calculated in the Corrugated Steel Plate Lining by the seismic load is decreased as the backfill height increases and the cut slope grows gentle. Also, the moment shows the tendency of decrease according to the increase of the backfill height. But in the case of the relative density of the backfill soil is small, the moment increases according to the increase of the backfill height and affects the dynamic behaviour characteristic. So it is considered that the relative density of the backfill soil is also the important point. As the result in analyzing the seismic response characteristics of the reinforcement spacing of the Corrugated Steel Plate, the variation in the compressive force is hardly happened, but the moment and the shear force increase on the reinforcement spacing being narrow.

• Nuclear Engineering and Technology
• /
• 제51권1호
• /
• pp.257-262
• /
• 2019

The control of microstructure is critical for the porous fuel particles used for infiltrating actinide nuclides. This study concerns the effect of heating processes on properties and microstructure of the fuel particles. The uniform gel precursor beads were synthesized by a microfluidic sol-gel process and then the porous $CeO_2$ microspheres, as a surrogate for the ceramic nuclear fuel particles, were obtained by heating treatment of the gel precursors. The fabricated $CeO_2$ microspheres have a narrow size distribution and good sphericity due to the feature of microfluidics. The effects of heating processes parameters, such as heating mode and peak temperatures on the properties of microspheres were studied in detail. An optimized heating mode and the peak temperature of $650^{\circ}C$ were selected to produce porous $CeO_2$ microspheres. The optimized heating mode can avoid the appearance of broken or crack microspheres in the heating process, and as-prepared porous microspheres were of suitable pore size distribution and pore volume for loading minor actinide (MA) solution by an infiltration method that is used for fabrication of MA-bearing nuclear fuel beads. After the infiltration process, $1000^{\circ}C$ was selected as the final temperature to improve the compressive strength of microspheres.

• Structural Engineering and Mechanics
• /
• 제85권3호
• /
• pp.337-351
• /
• 2023

In this paper, the shear behavior of soft filling in rectangular-hollow concrete specimens was simulated using the 2D particle flow code (PFC2D). The laboratory-measured properties were used to calibrate some PFC2D micro-properties for modeling the behavior of geo-materials. The dimensions of prepared and modeled samples were 100 mm×100 mm. Some disc type narrow bands were removed from the central part of the model and different lengths of bridge areas (i.e., the distance between internal tips of two joints) with lengths of 30 mm, 50 mm, and 70 mm were produced. Then, the middle of the rectangular hollow was filled with cement material. Three filling sizes with dimensions of 5 mm×5 mm, 10 mm×5 mm, and 15 mm×5 mm were provided for different modeled samples. The parallel bond model was used to calibrate and re-produce these modeled specimens. Therefore, totally, 9 different types of samples were designed for the shear tests in PFC2D. The shear load was gradually applied to the model under a constant loading condition of 3 MPa (σc/3). The loading was continued till shear failure occur in the modeled concrete specimens. It has been shown that both tensile and shear cracks may occur in the fillings. The shear cracks mainly initiated from the crack (joint) tips and coalesced with another one. The shear displacements and shear strengths were both increased as the filling dimensions increased (for the case of a bridge area with a particular fixed length).

• Journal of Preventive Medicine and Public Health
• /
• 제2권1호
• /
• pp.77-80
• /
• 1969

In the cities nowadays, the dwelling conditions of Cackroach are provided by use of various kinds of construction material, installation of heating and cooling facilities that maintain moderate temperature, filthy sanitation, and lack of knowledge about insect as mechanical Vector. Cakroach is infectious disease Vector, and it proves to be of much importance in the public health. Considering such importance, the author has surveyed the distribution of Cackroach in the housing areas of Seoul City from May 1969 to the end of August 1969, and has come to the following conclusion: 1. House dwelling Cackroach collected in the City of Seoul are of two species, i. e. Blatella Germanica Linneaus and Periplaneta Japonica Karny. 2. Most of cackroach collected in Seoul are Blatella Germanica Linneaus and they are distributed in whole area of Seoul while that of Periplaneta Japonica Karny is distributed only in the limited area. 3. Dwelling places of Blatella Germanica Lineaus are in grog shop, Korean food restaurants, bakery shops, and patient rooms in hospitals. Many of them are found in tile kitchens and dining rooms of restaurants, and tearooms. They live in groups at older houses with much crack, warm and humid places. 4. For method of collection, the hand collection was the most effective. In trap collection during the day time, when the trap is placed at the narrow corners off the ground after confirming the dwelling places of cackroach, the match trap was more effective than the flask trap in collecting. In case of collecting during the night time, the flask trap was much more effective method than the match trap.

• 한국식품영양과학회지
• /
• 제32권3호
• /
• pp.370-374
• /
• 2003

홍삼 분쇄의 신 가공 기술로서 비충격 분쇄방식인 cell cracker의 공장 적용 가능성을 제시하고 홍삼분말의 품질고급화에 기초자료로 활용하고자, 기존의 hammer mill(충격분쇄방식)과 cell cracker에 의한 분쇄방식으로 홍삼분말을 제조한 후 물성, 표면구조적 특성 및 관능적 특성을 측정하였다. 입도분석에서 sieve shaker로 분석한 결과, 100 mesh 이상은 모두 95%수준으로 비슷한 분포를 나타냈고 120 mesh 이상은 hammer mill로 분쇄한 홍삼분말이 높았으며 그 밖의 각 mesh별 입도분포는 큰 차이를 나타내지 않았다. Laser scattering analyzer로 분석한 결과 hammer mill로 분쇄한 홍분말의 입도분포는 최소 0.77$\mu\textrm{m}$에서 최대 128.07$\mu\textrm{m}$으로, cell cracker로 분쇄한 홍삼분말 4.24~180.07$\mu\textrm{m}$보다 분포가 넓었으며, 평균 입자 크기는 cell cracker로 분쇄한 홍삼분말이 크고 표준편차는 hammer mill로 분쇄한 홍삼분말이 크게 나타났다. 비표면적은 hammer mill로 분쇄한 홍삼분말이 1.42 $m^2$/g로 cell cracker로 분쇄한 홍삼분말 0.59 $m^2$/g보다 높게 나타났고, 표면구조적 특성은 hammer mill로 분쇄한 홍삼분말은 크고 작은 입자가 불균일하게 분포하고 있으며, 개별입자의 형태는 부등형의 거칠게 연마된 돌 모양에 가깝고 표면은 작고 부드러운 솜털모양을 하고 있는 반면에, cell cracker로 분쇄한 홍삼분말은 입자크기가 상대적으로 고르게 분포하고 있으며 개별입자의 형태는 부등형의 조각난돌 모양의 형태로 관찰되었다.

• 비파괴검사학회지
• /
• 제25권1호
• /
• pp.15-19
• /
• 2005

일반적인 와전류 검사는 단일 주파수 또는 매우 협소한 주파수 대역을 가지는 정현적 신호 사용하며, 알루미늄과 같은 도체에서 피로 균열 같은 결함을 검출하는데 사용되고 있다. 이에 반하여 펄스 와전류는 아주 넓은 주파수 대역폭을 가지는 펄스 신호를 사용한다. 이것은 여러 주파수를 동시에 사용하는 다중 주파수 와전류 검사를 한번에 수행할 수 있도록 하며, 일상적인 와전류 검사에 비하여 침투 깊이를 더 깊게 할 수 있다는 장점이 있다. 본 연구에서는 부식 또는 침식 등에 의한 금속 손실을 평가하기 위한 펄스 와전류 장치를 개발하였다. 개발된 장비는 최대 40 V의 구형 펄스를 발생시키는 펄스 발생기, 수신된 신호를 52 dB까지 증폭하는 증폭기, 16 bit 20MHz의 A/D 변환기, 윈도우 프로그램으로 운영되는 산업용 개인 컴퓨터로 구성하였다. 펄스 와전류 탐촉자는 구동 코일 안에 검출 코일을 삽입한 pancake 형태로 설계 제작하였다. 검출 코일의 출력 신호는 구동 코일에 전압을 끊을 때 갑자기 증가하고 신호의 후반부는 시간에 따라 지수적으로 감소하였으며, 감쇠율을 나타내는 지수 값은 알루미늄 두께가 두꺼울수록 증가하였다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.183-184
• /
• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.