• Korean Journal of Materials Research
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• v.8 no.5
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• pp.444-449
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• 1998

There are various shielding materials that have been considered; the use of a metallic plate or the layering of a conductive material on a plastic surface and the insertion of filler in plastics. All of these methods have shown their merits and weakness. Therefore, many studies have concentrated on developing materials that effectively cut down EMI without increase in weights of housing materials. In these respects, this study has focused on investigations of the shielding effect of materials that have electroless nickel plating on the lamella structured micro particles surface with low specific gravity. When a film of electroless nickel were plated on a micro particle surfaces and then mixed with paint, the electromagnetic shielding effects were measured as 63dB. Although these effects were less than that 90dB of the copper plate, trials in a series of 6 times increased the shielding effect by IOdB and is applicable to wide range of EMI shielding.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.67-74
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• 2005

This paper concerns attitude controller design for a 3-staged launch vehicle which has movable nozzle TVC systems for all stages as its control systems. The PD-type control gains are determined by shaping the corresponding closed-loop natural frequencies for the purpose of guaranteeing the required stability margin. Bending filters are also designed to stabilize the bending modes by using parametric optimization method. The designed controllers are verified using six degree of freedom flight simulations in MATLAB.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1211-1221
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• 1990

The purpose of this study is to get experimental data on the distribution of CWM (Coal- Water Mixture) droplets size and the presence of pulverized coal particles inside CWM droplets. Atomization of CWM is done by Twin-Fluid Atomizer. The operational parameters are atomizing air pressure, coal particle loading, mean size of pulverized coal particles and sampling positions across spray. Th data analysis is initiated by Impression Sampling Method(Magnesium Oxide Technique) and Photo-technique and counting works are followed. Experimental work induces following research results. The variation of particle loadings in slurry makes no appreciable effects on the mean size of CWM droplets. It is evident that atomizing air pressure has very strong effect on the atomization of slurry. The mean size of atomized fuel droplets is dramatically reduced with the increasing air pressure. The population ratio of droplets without coal particles to total number of droplets is decreased as atomizing air pressure or loading rises and the same trend is obtained as the mean size of coal particles becomes smaller but a certain tendency of coal particle presence inside droplets could not be found from the change of sampling positions.

• Honam Mathematical Journal
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• v.1 no.1
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• pp.61-75
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• 1979

In this explanation. we shall describle how the de Rham's cohomology on a n-dimensional $C^{**}$-manifold is constructed. The Čech's cohomology defined by only topological structure of $C^{**}$-manifold has a crack that it is dependent on the covering of a $C^{**}$-manifold. At the end of explanation we shall prove that the de Rham's cohomology is isomorphic to Čech's cohomology which is made by simply covering.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.487-492
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• 1998

Ultrafine particles of $SnO_2$ or $(Sn,Ti)O_2$ and thin films of $SnO_2$ were synthesized by introducing aqueous tin chloride solution into a high temperature argon inductively coupled plasma (ICP) generated under ambient pressure (the spray-ICP technique). As-deposited $SnO_2$ particles from each concentration of solution were all tetragonal $SnO_2$ crystallline phase and their mean size decreased in proportion to the increase of solution concentration. The mean size of $SnO_2$ particles was in the 10~40 nm range.

• Journal of the Society of Disaster Information
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• v.9 no.4
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• pp.469-475
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• 2013

The purpose of this experimental research is to estimate compressive strength and resistance to freezing and thawing of recycled aggregate concrete containing ground granulated blast furnace slag. For this purpose, concrete specimens according to substitution ratio of recycled aggregate were made for different replacement ratio of ground granulated blast furnace slag(GGBFS), and then compressive strength and resistance to freezing and thawing were evaluated for those. It was observed from the test results that compressive strength at 28 days of recycled aggregate concrete containing GGBFS of 20% was much more excellent than plain concrete and when air content of concrete was maintained 4 to 6%, influence of substitution ratio of recycled aggregate and replacement ratio of GGBFS on resistance to freezing and thawing was little up to 300 cycles of freezing and thawing.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.190-198
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• 2002

In this research the physical properties of polymer modified mortar containing pulverized FRP(Fiber-Reinforced Plastics) wastes fine powder as a part of fine aggregate were investigated. Styrene-butadiene rubber(SBR) latex, polyacrylic ester(PAE) emulsion and ethylene-vinyl acetate(EVA) emulsion were used as Polymer modifier. Polymer modified mortars containing FRP wastes fine powder were prepared with various FRP wastes fine powder replacement(5∼30 wt％) for fine aggregate and polymer-cement ratios(5∼20 wt％). The water-cement ratio, water absorption rates and hot water immersion test, compressive and flexural strengths of polymer modified mortars were tested and the results compared to those of ordinary portland cement mortar. As the results, compressive and flexural strengths of polymer modified mortar containing FRP wastes fine powder depend on the contents of FRP wastes fine powder, type and additional amounts of polymer modifier. Some of them showed higher compressive and flexural strengths than those of ordinary portland cement mortar. Especially, SBR-modified mortar showed the highest strengths properties among three types of polymer modifier. Also water absorption rates, compressive and flexural strengths of SBR-modified mortar were more superior than those of PAE or EVA-modified mortar. The optimum mix proportions of SBR-modified mortar was 20 wt％ of polymer-cement ratio and 20 wt％ of FRP wastes fine powder replacement. Otherwise heat cured polymer modified mortar accelerated the improvement of early compressive and flexural strengths.

• Communications of the Korean Mathematical Society
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• v.9 no.3
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• pp.671-686
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• 1994

다양체 M은 매끈하고(smooth) 콤팩트(compact) n 차원 리만다양체이고, 실가함수 f는 M상에서 미분가능 함수임을 가정한다. Morse 함수는 임계점(critical point)들이 모두 비퇴화(non-degenerate)인 실가함수이다. 만약 함수 f가 Morse 함수이고, 임의의 점 $x \in M$에서 $\gamma_x$는 x를 통과하는 흐름(flow)이면 $$ (*) \frac{d\gamma_x(t)}{dt} + \bigtriangledown_{\gamma x(t)}(f) = 0 $$ 이다. 여기서 $\bigtriangledown(f)$는 함수 f에 의해서 정의되는 기울기 벡터장이고 초기조건 $\gamma_x(0) = x$ 이다.

• Honam Mathematical Journal
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• v.1 no.1
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• pp.15-20
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• 1979

본(本) 논문(論文)에서는 smooth Affine variety가 미분가능(微分可能) 다양체(多樣體)임을 보임으로써 대수기하학(代數幾何學)이 다양체이론(多樣體理論)과 관련(關聯)됨을 논(論)하였다. $\S1$에서는 affine variety의 차원(次元)과 affine variety의 접공간(接空間)에 대(對)한 정의(正義)와 그에 관련(關聯)된 성질(性質)들을 논(論)하였고 $\S2$에서는 simple point와 국소(局所) 매개변수(媒介變數), 그리고 ${\Theta}_x$에서의 유리함수의 급수(級數) 등(等)을 이용(利用)하여 주정리(主定理)(정리(定理)9)를 증명(證明)하였다.

• Resources Recycling
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• v.11 no.2
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• pp.36-44
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• 2002

The waste garnet powder as a raw material for clay bricks was studied its recycling. The physical strength of clay bricks are closely dependent both on the contents of $SiO_2$, $Al_2$$O_3$, and $Fe_2$$O_3$in clay and on the viscosity of it. Although the garnet power has very high contents of $SiO_2$, $Al_2$$O_3$, and $Fe_2$$O_3$, it could not substituted to clay because of its low viscosity. Therefore the substitution of sand with waste garnet powder was considered to influence positively on the strength of clay bricks .Mixing ratios of {clay-sand}, {sand-garnet powder}, and {clay-sand-garnet powder} based on weight were controlled in the production of clay bricks. The properties of clay bricks such as compression strength, moisture absorption, shrinkage, and specific gravity has been evaluated. It was shown that the optimal mixing combination was found to be { clay(50%)-sand(30%)-garnet powder(20%)} as a weight basis. The present study indicated possibilities to produce commercially clay bricks with the waste garnet powder. An economical benefit will be produced in viable in view of recycling waste garnet powder.