• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.839-842
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC-ZrB$_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_2$O$_3$+Y$_2$O$_3$. Phase analysis of composites by XRD revelled $\alpha$ -SiC(6H), ZrB$_2$, and YAG(Al$_{5}$ Y$_3$O$_{12}$ ). Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism, the fracture toughness showed the highest value of 6.3MPa.m$^{1}$2/ for composites added with 24wt% $Al_2$O$_3$+Y$_2$O$_3$additives at room temperature. The resistance temperature coefficient respectively showed the value of 2.46$\times$10$^{-3}$ , 2.47$\times$10$^{-3}$ , 2.52$\times$ 10$^{-3}$ $^{\circ}C$ for composite added with 16, 20, 24wt% A1$_2$O$_3$+Y$_2$O$_3$additives. The electircal resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to 90$0^{\circ}C$.

• 원예과학기술지
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• 제18권2호
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• pp.103-106
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• 2000

RAPD 방법을 이용하여 국내자생 자란과 일본자생 자란의 유전적 다형성을 연구하였다. PCR 결과 156개의 재현성을 보이는 band를 얻었으며 그 중 58개가 다형성을 보였고 98개는 단일성을 나타냈다. 유연관계 분석 결과 자란은 세가지의 그룹으로 분류되었다. 첫 번째 그룹은 국내 A(자생일반종), B(목포산 자생 반엽종), C(자생 반엽종) 그리고 일본품종 D와 E(일본자생 일반종)가 속한다. 국내 무늬종 B와 C의 유사도 0.806, 일본품종 D와 E는 0.778로 매우 높게 나타났다. 두 번째 그룹은 일본품종 G(일본자생 왜성종)만이 분류되었다. 그리고 세 번째 그룹은 일본자생 무늬종인 F와 H(일본자생 무늬종)가 포함되었다.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.3292-3297
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• 2014

자동차의 와이퍼 블레이드(Wiper Blade, W/B)의 마찰계수를 낮추기 위하여 고무 표면을 염소 처리하였다. 염소처리 방법으로는 물 $20.0{\ell}$에 35.0% 염산(HCl)과 5.25% 차아염소산소다(NaOCl)를 각각 $300m{\ell}$, $400m{\ell}$를 첨가한 염소처리용액을 만든 후, 2분에서 20분 동안 처리하였다. 처리 후의 표면 특성은 IR 스펙트럼, 마찰계수 측정기, EPMA를 이용하였다. IR 스펙트럼으로 부터 W/B 고무 표면의 염소화 정도를 확인하였다. 마찰계수는 염소처리에 의해 크게 감소하였다. 특히, 염소화 초기에 보다 민감한 영향을 나타내었다. 고무표면 특성을 고무 파단면의 길이 방향에 대하여 EPMA 선분석한 결과를 얻었다. EPMA에 의한 염소침투깊이는 위의 염소농도에서, 염소처리를 5분 실시한 후에 1.2 ${\mu}m$ 임을 알 수 있었다.

• 대한조선학회지
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• 제11권1호
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• pp.9-16
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• 1974

To contribute towards more accurate estimation of the virtual inertia coefficient for the horizontal vibration of ships, three dimensional correction factor $J_H$ for the added mass of finitely long elliptic prismatic bars in horizontal vibration in a free surface of an ideal fluid are calculated. In the problem formulation Dr. T. Kumai's quasi-finite length concept[1,11,12] is employed. Now that, in Dr. Kumai's work[1] for the horizontal vibration the mathematical model was a circular cylinder, the principal aim of the authors' work is to investigate the influence of the beam-draft ratio B/T on $J_H$. The numerical results of this work are shown in Fig.3 graphically, from which we may recognize that the influence of B/T on $J_H$ is remarkable as much as that of the length-draft ratio L/T(refer to Fig.1 also). In Fig.3 the curves for B/T=2.00 are of those based on Dr. Kumai's result[1]. On the other hand, the experimental data obtained by Burril et al.[9] for the horizontal vibration of finitely long prismatic bars of various cross-section shapes are compared with the theoretical added mass coefficients defined by combination of the authors' $J_H$ from Fig.3 and two dimensional coefficients $C_H$ obtained by Lewis form approximation for the corresponding sections. They are in reasonable correspondence with each other as shown in Fig.2. Finally, considering that the longitudinal profile of full-form ship's hull is well resembled to that of an elliptic cylinder and that the influences of other factors such as the sectional area coefficient and the shape of section contour itself can be well merged in the two dimensional added mass coefficient, the authors recommend that the data given in Fig.3 may be successfully adopted for the three dimensional correction factor the added mass in the horizontal vibration of hull-form ships.

• 상하수도학회지
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• 제35권6호
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• pp.379-387
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• 2021

In general, trans-membrane pressure (TMP), flux, filtration resistance are used as indicators to evaluate the degree of fouling in MBR. However, they have limitations in determining the level of EPS generation, which is known as an important factor of fouling. Therefore, a new evaluation method is required to monitor the amount of EPS generation. In this study, the applicability of capillary suction time (CST), which is used to measure the dewaterability of sludge, was evaluated as an indirect fouling evaluation index. Statistical analysis was performed to evaluate the effect of EPS on CST, and to determine whether EPS has high similarity with representative fouling evaluation indicators and CST, and quantitatively compared them. As a result, the correlation coefficient between CST and bEPS was 0.7988, which was higher than the correlation coefficient between filtration resistance and bEPS. Since bEPS is a major factor inducing fouling by affecting the formation of the cake layer, it was evaluated that CST, which has a high correlation with bEPS, is suitable to represent EPS. In addition, it was evaluated that the correlation coefficient between filtration resistance and CST was high as 0.7187, which could be used as a fouling evaluation index.

• 설비공학논문집
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• 제6권1호
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• pp.39-46
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• 1994

Experiments on the performance of refrigeration system using alternatives to R12 are carried out. The condenser and the evaporator are concentric-tube heat exchangers of counter-flow type and the compressor is driven by a variable speed motor. In this study, R134a, R152a, R22/142b(50 : 50 by mass) are adopted as alternatives to R12. Tests are performed by varying the inlet and outlet temperatures of secondary fluids of evaporator and condenser under the condition of constant compressor speed, degree of superheating and degree of subcooling. Results show that R134a has refrigeration capacity close to that of R12 and requires the greatest compressor power compared with that of others. And the system using R152a shows the best performance from the viewpoint of refrigeration capacity, compressor power and coefficient of performance. R22/142b is superior to R12 in the above points.

• Journal of the Korean Wood Science and Technology
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• 제44권2호
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• pp.191-203
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• 2016

To investigate the dynamic sorptive and hygroexpansive behaviors of wood by different cyclic hygrothermal changing effects, poplar (populus euramericana Cv.) specimens, were exposed to dynamic sorption processes where relative humidity (RH) and temperature changed simultaneously in sinusoidal waves at 75-45% and $5-35^{\circ}C$ (condition A) and where RH changed sinusoidally at 75-45% but temperature was controlled at $20^{\circ}C$ (condition B), both for three cyclic periods of 1, 6, and 24 h. Moisture and dimensional changes measured during the cycling gave the following results: Moisture and transverse dimensional changes were generally sinusoidal. Moisture and dimensional amplitude increased with increasing cyclic period but all were lower for thicker specimens. The amplitude ratio of condition A to condition B ranged from 1.0 to 1.6 with the maximum value of 1.57 occurring at the shortest cyclic period, not as much as expected. T/R increased as cyclic period increased or specimen thickness decreased. T/R from condition B was weaker than that from condition A. Sorption and swelling hysteresis existed in both conditions. Sorption hysteresis was negatively related to cyclic period but in positive correlation with specimen thickness. Sorption hysteresis was found more obvious in condition B, while moisture sorption coefficient and humidity expansion coefficient showed the opposite results.

• 한국전자파학회논문지
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• 제10권6호
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• pp.866-878
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• 1999

본 논문에서는 원형 디스크와 두 개의 환 디스크로 구성된 페라이트 공진기를 갖는 스트럽라인 서률레이 터를 설계하고 제작한다. 순환 그런함수 가법을 이용하여 각 단자의 전자계를 구하고 입력 임피던스와 산란 행렬을 유도한다. 페라이트 공진기의 각 디스크에 대한 매질 배치에 따른 서율레이션 특성, 바이어스 필드의 세기에 따른 서률레이션 특성과 포트 단자의 폭에 따른 서률레이션 특성을 비교. 분석한다. 설계된 제원을 사용하여 제작한 서률레이터의 통과대역 주파수는 1.55 GHz에서 2.95 G Hz까지이고 입력 단의 반사계수 $S_{11}$ 은 공진접 2.38 GHz에서 30 dB, 아이솔레이션 단에서 입력 단으로의 전송계수 $S_{21}$은 - 28 dB로 나타났다

• Macromolecular Research
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• 제11권4호
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• pp.283-290
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• 2003

Organic drugs including aspirin, omeprazole, and naproxen with three different levels of octanol/water partition coefficient were examined for their release behavior from the amphiphilic PCL-b-PEO-b-PCL (PCEC) matrix. Scanning electron micrograph (SEM) of PCEC illustrated a well defined two-phase morphology consisted of dispersed poly(ethylene oxide) (PEO) domain and continuous polycaprolactone (PCL) phase. Differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) experiments veri tied that three model drugs are dissolved as a molecular dispersion in PCEC matrix. The release of hydrophilic aspirin closely followed the water absorption profile of the matrix indicating that its major fraction is present in PEO domain. However, substantial amount of aspirin present in less hydrophilic region displayed discontinuous biphasic release pattern. In the case of omeprazole with intermediate hydrophobicity consistent release behavior was observed for a period of 24 hrs after the rapid liberation of ca. 10% of the drug presumably partitioned in PEO phase. It was ascribed to the fact that the progressive hydration of PCEC matrix gradually increased the chance of drug/water exposure to compensate the exhaustion of device. Naproxen with the highest octanol/water distribution coefficient among three model drugs exhibited a limited release of 35% for 24 hrs. Finally, hydroxypropyl methylcellulose phthalate (HPMCP)/PCEC blend matrix demonstrated an accelerated and quantitative release of hydrophobic naproxen by generating high porosity and thereby expanding polymer/water interface.

• 한국통신학회논문지
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• 제38C권7호
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• pp.643-649
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• 2013

본 논문에서는 무선통신기기에서 필수적으로 사용되는 안테나의 근접 전자기장 변화에 의한 반사계수의 변화를 토대로 하여 사람의 심박신호를 검출한다. 반사되는 신호를 검출하기 위하여 20 dB의 directional coupler를 사용하여 송신신호에 영향을 주지 않고 안테나의 반사계수를 검출하는 회로를 사용하였다. 사람의 심박에 의한 다이폴 안테나의 반사계수는 약 0.07 dB 가량 변하게 되어 검출하기 어려우므로, 민감도를 향상시키는 방법을 적용하여 심박신호를 깨끗하게 잡아내었다. Discrete한 소자의 사용으로 오차가 발생하는 것을 감안하여 안테나의 위치를 움직여 최적 지점에서 더 좋은 심박신호의 결과를 나타내는 것을 확인하였고, 일반적인 통신신호에서도 가능한지 확인하기 위하여 4 MHz 대역의 FM신호를 사용하여 잘 동작하는 것을 검증하였다.