• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.605-608
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• 1999

The objective of this research is to examine whether the determination of development length for high strength concrete by the ACI Building Code 318-95 could be applied and the upped limit of compressive strength, 700kg/$\textrm{cm}^2$ is suitable. Eight beam specimens were tested. Each beam was designed to include two bars in tension, spliced at the center of the span. The beams were loaded in positive bending with the splice in a constant moment region. The variables used here were compressive strength and the space of stirrup within splice length. The results indicated that for (c$\div$Ktr)/db of the range of 1.5-2.0 compressive strength up to 800kg/$\textrm{cm}^2$ is acceptable with regard to bond strength and ductility, thus the limit of compressive strength in ACI 318-95 may be extended to 800kg/$\textrm{cm}^2$.

• Bulletin of the Korean Chemical Society
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• 제28권8호
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• pp.1363-1370
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• 2007

The geometrical structures of pyridazin-3-one derivatives (4,5-dihalopyridazin-3-one and 4-halo-5- alkoxypyridazin-3-one) with various functional and substituent groups were fully optimized using the ab initio Hartree-Fock (HF) and second order Moller-Plesset perturbation (MP2) methods. At the N2-, C4-, and C5- positions on the pyridazin-3-one rings, the structural and electronic features pertaining to the variations of the functional and substituent groups were analyzed, respectively. The trends in the variation of the bond lengths, atomic charges, and energetics (relative energy, binding energy) of the derivatives induced by changing the electron donating functional groups (X1 = OMe, OEt) to electron withdrawing groups (X1 = Cl, NO2) were examined. The variations of the bond lengths, atomic charges, and binding energies with the electron withdrawing strength of the substituent groups (Y = Me → F) were also investigated.

• 한국구조물진단유지관리공학회 논문집
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• 제21권1호
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• pp.134-141
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• 2017

시멘트 생산 과정에서 생성되는 이산화탄소 배출량을 감소시키기 위하여 시멘트를 대체할 수 있는 건축 재료 개발에 많은 연구가 진행되어왔다. 시멘트 대체재로 사용될 수 있는 활성 황토는 $850^{\circ}C$에서 소성 과정을 거쳐 제작된다. Poly-Vinyl Alcohol(PVA) 섬유와 GFRP 보강근은 활성 황토 콘크리트의 균열 문제를 해결하기 위하여 사용된다. 본 논문은 PVA 섬유 보강 활성 황토 콘크리트에 대하여 인발 하중에 따른 GFRP 보강근의 부착 성능을 평가하기 위한 실험 연구를 나타내고 있다. 실험 결과, 황토가 치환된 PVA 보강 및 무보강 실험체들의 평균 부착 응력 계수가 2.27~2.48로 나타났으며, 부착 응력 계수가 PVA 섬유 보강 유무 및 황토 치환율에 크게 영향을 받지 않는 것으로 나타났다. 그리고 부착 길이가 길어질수록 부착 강도는 저하되었다.

• 한국진공학회지
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• 제7권1호
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• pp.5-10
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• 1998

CAICISS장치를 이용하여 깨끗한 Si(001) 표면에서 재배열하는 dimer의 원자구조를 분석하였다. Si(001) 표면에서 dimer원자가 확실히 buckled되어 있음을 확인하였고, asymmetry(2$\times$1)구조와 c(4$\times$2)구조가 공존하고 있음을 밝혔다. dimer원자의 결합거리는 2.3$\pm$0.1$\AA$이고, buckling각은 18$\pm$$1^{\circ}$였다.

• 대한화학회지
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• 제21권5호
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• pp.307-319
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• 1977

Thiourea derivative인 $N-({\alpha}-dimethyl\;{\beta}-hydroxy)ethyl\;N'-cyclohexyl\;thiourea,\;C_{ll}H_{22}N_2OS)$의 결정 및 분자구조를 X-선 회절법으로 해명하였다. 이 화합물의 결정은 공간군 $P_{bca}$에 속하는 orthorhombic 형으로 a = 10.33(3), b = 11.82(3), c = 22.57(4)${\AA}$ 이고 Z = 8이다. Weissenberg 사진촬영으로 얻은 회절반점의 총수는 1414개이며 중원자법을 이용하여 구조해명을 한 후 최소자승법으로 정밀화하였으며 최종 R값은 0.13이다. Cyclohexane ring은 normal chair conformation을, thiourea 부분은 평면을 이루고 있다. 일차 알코올의 hydroxyl group은 N(2)원자와 분자내 수소결합을 이뤄서 전체분자를 안정화시키고 있다. 분자들은 결정내에서 수소결합과 van der Waals힘으로 서로 결합되어 있다. 분자내 수소결합 N(2)-H${\cdot}{\cdot}{\cdot}$O는 강한 수소결합으로 N${\cdot}{\cdot}{\cdot}$O 길이는 2.71${\AA}$이고, 분자간 수소결합 O${\cdot}{\cdot}{\cdot}$H${\cdot}{\cdot}{\cdot}$S의 O${\cdot}{\cdot}{\cdot}$S 길이는 3.02${\AA}$으로 b축에 나란하다.

• 대한치과교정학회지
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• 제23권1호
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• pp.75-88
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• 1993

Recent reports indicate that shorter etching times than 60 seconds can be adopted without affecting the bond strength and clinical disadvantages. The purpose of this in vitro study was to compare the shear bone strength and to measure depth of etch at different etching time length. One hundred and eight extracted bovine lower central incisors were embedded each in a tooth cup with cold-cure acrylic resin. The facial surfaces of the teeth were ground wet with 600-, 800-, 1000-, and 1200-grit Sic papers, and finally polished with a water slurry of extrafine silicon carbide powder, washed with tap water, and dried with hot air. Nine groups of nine prepared teeth were etched with a commercial($38\%$ phosphoric acid solution) for 0, 5, 10, 15, 20, 30, 60, 90, and 120 seconds, respectively, rinsed with tap water, and dried with hot air. One conditioned teeth from every group was selected randomly for the scanning electron microscopic examination, and the remaining eight teeth of the groups were used for measuring the push shear bond strength after bonding brackets and immensing them in the $36.5^{\circ}C$ water for 24 hours. Another nine groups of three teeth were used for measuring the depth of etch and surface roughness with a surface profilometer. after pieces of adhesive tape of 3mm inner diameter positioned on the ground enamel surfaces, and etched with the above mentioned. The data obtained form the above expeiments were analysed statistically with one way ANOVA and Dunkan's multiple range test with the $95\%$ confidence level. The results and conclusion of the study were as follows; 1. The results of shear bond strength for the given experimental etching times were not statistically different, but showed the tendency of decreasing shear bone strength after over 60 seconds etching times. 2. On the scanning election microscopic examination, it was observed that the morphological patterns of etched enamel surface for 5 to 20 seconds were similar and consitent, and those for 30 to 120 seconds showed increasing over-etched patterns depending on the length of etching times. 3. The depth of etch was increased almost proportionally by the length of etching times, but it was not associated with the shear bond strength. 4. The surface roughness increased depending on the length of etching times, but it was not associated with the shear bond strength. 5. This experiment indicated that proper etching time with $38\%$ phosphoric acid solution is in the range of 5 to 30 seconds.

• Bulletin of the Korean Chemical Society
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• 제19권9호
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• pp.947-951
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• 1998

$K_2NiF_4$-type layered compounds of the ($C_nH_{2n+1}NH_3)_2SnCl_4$ (n=2, 4, 6, 8, and 10) system have been synthesized from a stoichiometric mixture of $SnCl_2$ and alkyl ammonium salt using a low temperature solution technique under the inert atmosphere condition. Their crystal structures are assigned to the orthorhombic system by X-ray powder diffraction analysis. The a and b cell parameters show small changes. However, the c parameter is varied significantly according to the increment of alkyl chains of the organic layer which is located between inorganic layers in the compounds. The conformational phase transitions of the compounds are studied by the DSC in the temperature range of 300 to 500 K. FT-IR and Raman spectra are analyzed in the ranges of 1300 to 4000 cm-1 and of 50 to 360 $cm^{-1}$ with Ar-laser (λ=514.5 nm) excitation, respectively. Photoluminescence phenomena are observed for some compounds. The bond-length of Sn-Cl is determined by the EXAFS spectroscopic analysis.

• Computers and Concrete
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• 제21권3호
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• pp.249-259
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• 2018

The use of recycled aggregate in concrete is gaining much attention due to the growing need for sustainability in construction. In the present study, Self Compacting Concrete (SCC) is made using both natural and recycled aggregate (crushed recycled concrete aggregate from building demolished waste) and performance of recycled aggregate based SCC for the bond behaviour of reinforcement is evaluated. The major factors that influence the bond like concrete compressive strength (Mix-A, B and C), diameter of bar ($D_b=10$, 12 and 16 mm) and embedment length of bar ($L_d=2.5Db$, $5D_b$ and full depth of specimen) are the parameters considered in the present study in addition to type of aggregates (natural and recycled aggregates). The mix proportions of Natural Aggregate SCC (NASCC) are arrived based on the specifications of IS 10262. The mix proportions also satisfy the guidelines of EFNARC. In case of Recycled Aggregate SCC (RASCC), both the natural coarse and fine aggregates are replaced 100% by volume with that of recycled aggregates. These mixes are also evaluated for fresh properties as per EFNARC. The hardened properties like compressive strength, split tensile strength and flexural strength are also determined. The pull-out test is conducted as per the specifications of IS 2770 (Part-1) for determining the bond strength of reinforcement. Bond stress versus slip curves were plotted and a typical comparison of RASCC is made with NASCC. The fracture energy i.e., area under the bond stress slip curve is determined. With the use of recycled aggregates, reduction in maximum bond stress is noticed whereas, the normalised maximum bond stress is higher in case of recycled aggregates. Based on the experimental results, regression analysis is conducted and an equation is proposed to predict the maximum bond stress of RASCC. The equation is in good agreement with the experimental results. The available models in the literature are made use to predict the maximum bond stress and compare the present results.

• Bulletin of the Korean Chemical Society
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• 제13권3호
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• pp.296-306
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• 1992

$^{13}C$ spin-lattice relaxation times were measured for n-alkanes of moderate chain length, ranging from n-octane to n-dodecane, under the condition of proton broad-band decoupling within the temperature range of 248-318 K in order to gain some insight into basic features of segmental motions occurring in long chain ploymeric molecules. The NOE data showed that except for methyl carbon-13 dipole-dipole interactions between $^{13}C$ and directly bonded $^1H$ provide the major relaxation pathway, and we have analyzed the observed $T_1data$ on the basis of the internal rotational diffusion theory by Wallach and the conformational jump theory by London and Avitabile. The results show that the internal rotational diffusion constants about C-C bonds in the alkane backbone are all within the range of $10^9\;-10^10\;sec^{-1}$ in magnitude while the mean lifetimes for rotational isomers are all of the order of $10^{-11}\;-10^{-10}$ sec. Analysis by the L-A theory predicts that activation energies for conformational interconversion between gauche and trans form gradually increase as we move from the chain end toward the central C-C bond and they are within the range of 2-4 kcal/mol for all the compounds investigated.

• 대한화학회지
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• 제38권7호
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• pp.509-515
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• 1994

고리(12C4, 15C5, 18C6, DT18C6, DA18C6) 및 비고리$(Q_2O_5)$ 폴리에테르와 11가지의 1차 및 2차 알킬암모늄 이온과의 상호작용을 NMR 적정과 전기전도도법으로 조사하였다. 모든 알킬암모늄 이온은 크라운 에테르 및 비고리 폴리에테르와 수소결합에 의해 비교적 안정한 1:1 착물을 형성하였다. 알킬암모늄 이온과 동공의 크기가 다른 동일계열 호스트와의 상호작용의 세기는 18C6 > 15C5 > 12C4 순이었으며, 알킬암모늄 이온에 대한 호스트 주개원자의 세기는 N > O > S 순이었다. 18C6는 2차 알킬암모늄 이온에 비해 1차 알킬 암모늄 이온과 더 강한 상호작용을 하는 반면, DA18C6는 2차 알킬암모늄 이온과 더 강한 상호작용을 하였다. 또한 25$^{\circ}C$ 메탄올에서 18C6와 알킬암모늄 이온과의 착물형성에 대한 안정도 상수를 전기전도도법에 의해 구하였다. 착물의 안정도는 주로 알킬암모늄의 차수(또는 수소결합 수), 알킬기의 길이, 알킬기의 구조에 의한 입체장애 등에 의해 크게 영향을 받았다.