• 한국세라믹학회지
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• 제26권4호
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• pp.514-520
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• 1989

The early hydration characteristics according to the C3S/C3A ratio and presence of gypsum, in order to establish the hydration mechanism of the system C3S-C3A, have been studied. The rate of C3S dissolution in the system C3S-Gypsum was higher than that in the system C3S. Consequently, the induction period was reduced and the rate of Ca(OH)2 formation in the accleration period was increased. The hydration of C3S in the system C3S-C3A was retarded because Al3+ in the liquid phase originating from the hydration of C3A was incorporated into calcium hydrosilicates formed. The retardation phenomenon of C3S hydration was not appeared in the system C3S-C3A-gypsum because the reaction of monosulfate formation became the rate-determining step.

• 한국강구조학회 논문집
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• 제18권5호
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• pp.643-654
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• 2006

본 연구에서는 iTECH 합성보 실험체에 대한 온도와 변형에 대한 내화성능을 ISO834 표준화재와 BS476-20 및 KSF2257 기준에 근거하여 평가하였다. 국내외적으로 복합구조의 내화성능을 규명하기 위한 연구는 지극히 미흡한 실정이며, 따라서 본 연구에서는 iTECH 합성보의 내화성능을 평가하기 위해 1.5m의 슬래브를 포함한 4..7m의 스팬길이에 대하여 실험을 수행하였다. 변수는 실험체의 단면크기, 피복재 보강방법과 보강두께, 그리고 하중비로 하여 내화실험을 수행하였다.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.265-269
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• 1995

Complexation of ortho-xylyl-17-crown-5 (X17C5) with alkali metal ions in acetonitrile was studied by 7Li and 23Na NMR spectroscopy. The complex formation constants of X17C5 with LiI, LiSCN, NaI, and NaSCN were determined by investigating the changes in the chemical shifts as a function of the concentration ratio of X17C5 to metal ion. It was found that X17C5 forms 1:1 complex with Li+ and Na+ ions and the log Kf's for the complexation with LiI, LiSCN, NaI, and NaSCN were determined to be 2.88, 2.43, 2.53, and 2.30, respectively. In particular, the kinetics of complexation of X17C5 with Na+ was investigated by the method of 23Na NMR lineshape analysis. Activation energies were determined from Arrhenius plot of the resultant rate constant data to be 25.4 kJ/mol for NaI and 15.1 kJ/mol for NaSCN. Other kinetic parameters were also calculated by employing the Eyring equation. The decomplexation rates measured were 1.82 × 104 M-1s-1 for NaI and 1.50 × 104 M-1s-1 for NaSCN. It is concluded that the decomplexation mechanism is predominantly a bimolecular cation exchange for both cases.

• 대한환경공학회지
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• 제28권6호
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• pp.603-612
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• 2006

연안 대수층에 발생하는 해수침투를 효과적으로 방지하기 위한 대책으로서 인공 하수처리수의 대수층 함양수로의 가능성을 평가하고자 sand box를 이용한 실험실 규모의 연구를 수행하였다. 이를 위하여, 인공 대수층 내에서 다양한 양수 및 주입 조건에 따른 수리화학적 거동 특성을 평가하였다. 염수의 침투는 함양과 양수가 동시에 이루어질 때보다 양수가 없이 단지 함양만 이루어진 경우 더욱 저지되었다. 양수량과 함양량의 비가 $0.5{\sim}2$인 경우, 양수에 의하여 담수대로 침투하는 염수가 인공 수조 밖으로 배출됨과 동시에 함양에 의하여 함양관 주위로 형성된 수리화학적 방벽에 의하여 그 빈 공간은 함양수로 채워져 희석되어 해수침투가 후퇴되었다. 그러나 양수량이 함양량에 비하여 약 4배 이상인 경우 양수로 인한 빈 공간을 채울 만큼 함양량이 불충분해 염수는 담수대로 더욱 깊숙히 침투하였다. 양수량과 함얌량의 비가 $0.5{\sim}2$인 간헐적인 양수의 경우 S.M.I.값은 감소하였지만 그 비가 4이상인 경우 S.M.I.값은 $3{\sim}47%$로 오히려 증가하여 해수 침투가 진행됨을 나타내었다. 결론적으로 적절한 비율의 인공함양 혹은 간헐 양수방식을 채택할 경우 지하 대수층의 담수 자원을 안정적으로 이용하는 동시에 해수 침투를 효율적으로 방지할 수 있음을 확인하였다.

• 한국분무공학회지
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• 제2권4호
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• pp.7-14
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• 1997

Laser Raman scattering method has been applied to measure equivalence ratio of methane/air mixture in injected spray. We used high power KrF excimer laser$(\lambda=248nm)$ and a high gain ICCD camera to capture low intensity signal. Raman shifts and Raman scattering cross -sections of $H_2,\;O_2,\;N_2,\;CO_2,\;CH_4\;and\;C_3H_8$ are measured precisely. Our results show an excellent agreement with those of other groups. Mole fraction measurement of $O_2\;and\;N_2$ from air shows that $O_2:N_2=0.206:0.794$. We used gas injector which was operated at 1 bar. Methane is used as a fuel. Spray region is $10mm\times37mm$ and this region is divided into 80 points. In Raman signals are obtained and ensemble averaged for each point. 3-d and contour plot of distribution of equuivalence ratio is presented. Our measured results show that the equivalence ratio of methane/air mixture in methane-rich region is reasonable. However, more study is necessary for methane-lean region because background noise level is almost same as Raman intensity of methane.

• Earthquakes and Structures
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• 제3권5호
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• pp.749-766
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• 2012

Structural control through integration of passive damping devices within the building structure has been increasingly implemented internationally in the last years and has proven to be a most promising strategy for earthquake safety. In the present paper an alternative configuration of an innovative energy dissipation mechanism that consists of slender tension only bracing members with closed loop and a hysteretic damper is investigated in its dynamic behavior. The implementation of the adaptable dual control system, ADCS, in frame structures enables a dual function of the component members, leading to two practically uncoupled systems, i.e., the primary frame, responsible for the normal vertical and horizontal forces and the closed bracing-damper mechanism, for the earthquake forces and the necessary energy dissipation. Three representative international earthquake motions of differing frequency contents, duration and peak ground acceleration have been considered for the numerical verification of the effectiveness and properties of the SDOF systems with the proposed ADCS-configuration. The control mechanism may result in significant energy dissipation, when the geometrical and mechanical properties, i.e., stiffness and yield force of the integrated damper, are predefined. An optimum damper ratio, DR, defined as the ratio of the stiffness to the yield force of the hysteretic damper, is proposed to be used along with the stiffness factor of the damper's- to the primary frame's stiffness, in order for the control mechanism to achieve high energy dissipation and at the same time to prevent any increase of the system's maximum base shear and relative displacements. The results are summarized in a preliminary design methodology for ADCS.

• Journal of Welding and Joining
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• 제16권3호
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• pp.111-120
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• 1998

To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

• 한국통신학회논문지
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• 제27권4B호
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• pp.275-280
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• 2002

인터넷 서비스 및 이동통신 서비스 등에 대한 사용자들의 더 많은 욕구를 충족시키기 위하여 무선통신은 많은 발전을 거듭해 왔다. 그 중에서 차세대 무선통신을 주도할 인프라 중의 하나가 HAPS(High Altitude Platform Station : 성층전 통신시스템)이다. 본 논문에서는 이러한 HAPS를 사용하여 이동통신 시스템을 구축하였을 때의 오수신 확률에 대해 분석하였다. 먼저, 반송파 대 간섭 전력비를 파라메타로 하는 오수신확률을 유도하고, 이에 대한 해석결과를 수치계산 및 시뮬레이션하였다. 그 결과, 오수신 확률은 반송파 대 간섭 전력비(C/I)와 페이딩 심도(K)에 의해 큰 영향을 받게 되어, 일정한 C/I에 대해 K가 증가할수록, 일정한 K에 대해 C/I가 증가할수록 감소되어짐을 확인할 수 있었다. 또한, 앙각 30$^{\circ}$를 가지는 하나의 비행선 모델을 24개의 비행선 모델로 확장하면, 상대적으로 많은 간섭 원으로 인해서 반송파 대 간섭 전력비가 나빠짐을 알 수 있었다.

• 한국자동차공학회논문집
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• 제5권2호
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• pp.60-68
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• 1997

Rayleigh Scattering Cross Sections($\sigma$i) of various gases and the temperature distributions of premixes C3H8/O2 flame are measured by high power KrF(248nm) Exci- mer laser and ICCD camera. Results show that $\sigma$i of O2 and Propane(C3H8) gases agree well in the 5% error range, but of H2 has the more or less difference from the calcul- ated value by other groups. This is attributed to the low RS signal of H2 to Nosie level(S/N ratio). The temperature distributions of flame range out between 300K in the air and about 2000K in the burned area. In this temperature range, out system has the about 250K temperature resolution. Because low RS signals in the reaction area with high temperature are affected highly by noises, temperature uncertainty of this area is relatively high to another part of flame. Experimental results show that UV Rayleigh Scattering can be used for the measurement of mixing ratio of mixed gases and the temperature distributions of flame. Especially, this technique can be applied for the measurement of the mixing ratio of air/fuel before the ignition and the flame structure after the ignition inside the Engine.

• Asian-Australasian Journal of Animal Sciences
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• 제14권9호
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• pp.1238-1244
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• 2001

Two calorimetric experiments were performed to investigate the effects of two diets with same concentrate: roughage ratio (70:30) but varying in composition on energy metabolism and methane production in faunated (F) and defaunated (DF) Muzaffarnagari sheep. For experiment I, ten animals were divided equally into two groups of which one was kept normally F as such while other was DF using 10% sodium lauryl sulphate. All the animals were offered diet I which comprised of oat hay and concentrate mixture I (CM I) containing maize grain (93%) as a major ingredient in 70:30 ratio. Similarly, the experiment II was conducted for which four F and four DF sheep (same as used for experiment I) were switched to diet II that consisted of maize hay and CM II (maize grain 59% + molasses 36%). Through diet II, DM intake in DF sheep was significantly (p<0.05) lower. Intake of GE through both the diets was similar in F and DF sheep. Digestibility of DM, OM, CP and GE and also metabolisability (ME/GE) was similar in F and DF sheep on both the diets. Total urinary energy loss did not differ in F and DF on both the diets, but methane energy loss as a percent of GE in DF was significantly (p<0.05) lower on diet I (3.75 vs 2.48), while it did not differ on diet II (3.20 vs 3.60). Heat production was significantly (p<0.01) reduced in DF on both the diets. Although, efficiency of utilisation of ME for maintenance calculated as per ARC (1984) did not differ in F and DF on both the diets, efficiency for maintenance and growth was higher (0.60 vs 0.672) on diet I in DF. It was inferred that methane production in DF sheep reduces on good quality hay-based diet supplemented with slowly fermentable carbohydrate (maize grain) but supplementation of molasses (rapidly fermentable CHO) nullify this effect when sheep were fed diets with concentrate: roughage ratio of 70:30.