• Bulletin of the Korean Chemical Society
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• 제8권4호
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• pp.341-344
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• 1987

The fluorescence quantum yield of khellin is sensitive to temperature and to the nature of solvents, especially the proton-donating ability in solute-to-solvent hydrogen bonding. The intersystem crossing quantum yields are 0.4 and 0.15 in acetonitrile and ethanol, respectively. The fluorescence quantum yields in ethanol and isopentane at 77 K are 0.61 and 0.07, respectively, both of which are much larger than the values at room temperature. The phosphorescence lifetime is relatively long and decreases with decreasing solvent polarity. The phosphorescence to fluorescence quantum yield ratio is very small and remains unchanged in various solvents. The results suggest that internal conversion is an important decay channel of the excited singlet state of khellin, especially in the hydrogen-bonding hydroxyl solvents.

• Bulletin of the Korean Chemical Society
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• 제9권3호
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• pp.171-175
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• 1988

The spectral properties of piroxicam in different solvents are similar to those of its skeletal precursor, HMBDC. The maximum absorption and emission wavelengths strongly depend on the hydrogen bonding ability of the solvent, and it is shown that intramolecular hydrogen bonding between the -OH and the ortho carbonyl group of the parent benzothiazine ring plays an important role in the solvent-dependence of their spectroscopic properties. The fluorescence spectra in aprotic nonpolar solvent exhibit abnormally large Stokes-shifted (${\sim}9,000cm^{-1}$) emission bands in contrast to the spectra in water. In ethanol, dual emission bands with two different fractional components of lifetimes have been observed. These results suggest that the abnormally red-shifted emission is attributed to the proton transferred form of an intramolecularly hydrogen-bonded closed conformer.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2251-2255
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• 2013

Second-order rate constants ($k_{HOO^-}$) for the nucleophilic substitution reactions of Y-substituted-phenyl diphenylphosphinates (4a-4i) with $HOO^-$ in $H_2O$ have been measured spectrophotometrically. The ${\alpha}$-nucleophile $HOO^-$ is 10-70 times more reactive than the reference nucleophile $OH^-$ although the former is ca. $4pK_a$ units less basic than the latter, indicating the ${\alpha}$-effect is operative. The Bronsted-type plot for the reactions of 4a-4i with $HOO^-$ is linear with ${\beta}_{lg}=-0.51$, a typical ${\beta}_{lg}$ value for reactions which were reported to proceed through a concerted mechanism. The Yukawa-Tsuno plot is also linear with ${\rho}=1.40$ and r = 0.47, indicating that a negative charge develops partially on the O atom of the leaving group, which can be delocalized to the substituent Y through resonance interactions. Thus, the reactions have been proposed to proceed through a concerted mechanism. The magnitude of the ${\alpha}$-effect (i.e., the $k_{HOO^-}/k_{HO^-}$ ratio) decreases linearly as the leaving-group basicity increases. It has been concluded that solvation effect is not solely responsible for the ${\alpha}$-effect found in this study but the transition-state stabilization through an intramolecular H-bonding interaction is also responsible for the ${\alpha}$-effect.

• 대한치과보철학회지
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• 제18권1호
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• pp.49-57
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• 1980

The adhesive mechanisms on the metal-ceramic restorations have been reported to be mechanical interlocking, chemical bonding, compressive force, and Van der Waal's force, etc. Of these, the mechanical interlocking and chemical bonding forces are thought to affect the adhesive force between Ni-Cr alloy and porcelain. This study investigates the adhesion of Ni-Cr alloy to porcelain according to surface treatment. For this purpose, the following experiments were made; The compositions of Ni-Cr alloy as cast by emission spectrograph, and the oxides produced on Ni-Cr alloy during degassing at $1850^{\circ}F$ for 30 minutes in air and in vacuum were analyzed by X-ray diffractograph. The metal phases of Ni-Cr alloy were observed according to porcelain-baking cyclic heat treatment by photo microscope and the distribution and the shift of elements of Ni-Cr alloy and porcelain and the failure phases between Ni-Cr alloy and porcelain by scanning electron microscope. The adhesive force between Ni-Cr alloy and porcelain was measured according to surface treatment with oxidization and roughening by Instron Universal Testing Machine. Results were as follows; 1. The metal phases of Ni-Cr alloy as cast and degassing state showed the enlarged and fused core, but when subjected to porcelain-baking cyclic heat treatment, showed a dendrite growing. 2. The kinds of metal oxides produced on Ni-Cr alloy during degassing were found to be NiO and $Cr_2O_3$. 3. The distribution of elements at the interface of Ni-Cr alloy and porcelain in degassing state showed demarcation line, but in roughening state, showed mechanical interlocking phase. 4. The shift of elements at the interface occurred in both states, but the shift amount was found to be larger in roughening than in degassing. 5. The adhesive force between Ni-Cr alloy and porcelain was found to be $3.45{\pm}0.93kg/mm^2$, in degassing and $3.82{\pm}0.99kg/mm^2$, in roughening. 6. The failure phase between Ni-Cr alloy and porcelain showed the mixed type failure.

• Structural Engineering and Mechanics
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• 제34권4호
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• pp.449-474
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• 2010

A smart hollow cylinder consisting of a host functionally graded elastic core layer and two surface homogeneous piezoelectric layers is presented in this paper. The bonding between the layers can be perfect or imperfect, depending on the parameters taken in the general linear spring-layer interface model. The effect of such weak interfaces on free vibration and steady-state response is then investigated. Piezoelectric layers at inner and outer surfaces are polarized axially or radially and act as a sensor and an actuator respectively. For a simply supported condition, the state equations with non-constant coefficients are obtained directly from the formulations of elasticity/piezoelasticity. An approximate laminated model is then introduced for the sake of solving the state equations conveniently. It is further assumed that the hollow cylinder is embedded in an elastic medium and is simultaneously filled with compressible fluid. The interaction between the structure and its surrounding media is taken into account. Numerical examples are finally given with discussions on the effect of some related parameters.

• Journal of the Korean Wood Science and Technology
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• 제34권3호
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• pp.22-29
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• 2006

친환경 건축자재에 대한 관심이 높아짐에 따라서 가구 및 건축 내외장재로 사용되는 목질복합재료에 대한 친환경적 성능에 대한 요구는 점차 커져가는 추세이다. 목질 복합재료는 일반적으로 그 자체로 사용하기 보다는 표면재를 붙여서 사용하는데 이때 사용되는 요소포름알데히드 접착제를 친환경적인 SIS계 핫벨트 점착제로 대체코자 하는 데 이 연구의 목적이 있다. 본 연구에서는 기질고분자의 diblock 함량, 점착부여수지의 연화점 및 함량 등을 변화시키면서 여러 종류의 핫벨트 점착제를 제조하고 각각의 점착제에 의한 무늬목 부착성능을 평가함으로써 점착형 표면재에 대한 가능성을 제기하였다.

• 한국통신학회논문지
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• 제36권5A호
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• pp.536-542
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• 2011

FCC는 디지털 방송 전환 후 발생되는 TVWS에서의 효율적인 스펙트럼 활용을 위해 비면허 시스템의 주파수 사용을 허용하였다. 다양한 면허 사용자 및 비면허 CR 사용자가 공존하는 환경에서 최적 채널 선택을 위해서는 우선 채널 사용 현황 파악이 요구된다. 데이터베이스를 통해 제공되는 면허 사용자 채널 정보 외에는 센싱 알고리즘을 통한 검출이 필요한데 본 논문에서는 단일 채널 수신만으로 채널 본딩된 비면허 CR 신호까지 검출할 수 있는 알고리즘을 제안하였다. 전산 모의 실험 결과 IEEE 802.11af 신호는 단일 채널의 경우에는 SNR=-18dB, 8 채널 본딩 신호의 경우에는 SNR=-7dB에서 검출 확률이 90% 이상으로 나타났으며, 동일 조건에서 ECMA 392 신호는 단일 채널의 경우에는 SNR=-14dB, 8 채널 본딩 신호의 경우에는 SNR=-6dB로 나타났다. 결과적으로 제안 알고리즘을 통해 단일 채널 수신만으로 채널 본딩 신호의 검출이 가능해짐으로써 전채널 센싱 소요 시간의 감소 및 시스템 오버헤드를 줄일 수 있을 것으로 기대된다.

• 한국재료학회지
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• 제25권5호
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• pp.215-220
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• 2015

The effect of Al content on the processing of reaction-bonded $Al_2O_3$ (RBAO) ceramics using 40v/o ~ 80v/o Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processes that use ~ 40v/o pure Al powder. The influence of high Al content in starting $Al_2O_3$-Al alloy powder mixtures on its particulate characteristics, reaction-bonding, microstructure, physical and mechanical properties was revealed. Starting $Al_2O_3$-Al alloy powder mixtures with 40v/o ~ 80v/o Al alloy powder were milled, reaction-bonded, post-sintered, and characterized. With an increasing Al alloy content, the milling efficiency of Al alloy powder was lowered, resulting in a larger particle size after milling. However, in spite of the larger particle size of Al alloy powder, the oxidation, i.e., reaction-bonding, of the Al alloy was successfully completed via solid and liquid state oxidation, in which the activation energy of the oxidation was nearly the same regardless of Al alloy content. After reaction-bonding and post-sintering at $1600^{\circ}C$, RBAO ceramics from 80v/o Al alloy content showed a relative density of ~97% and a flexural strength of 251 MPa compared to ~ 96% and 353 MPa for RBAO ceramics from 40v/o Al alloy content, respectively. The lower flexural strength at 80v/o Al alloy content was due to the weak spinel phase that formed from Zn, Mg alloying elements in Al.

• 대한화학회지
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• 제22권3호
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• pp.111-116
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• 1978

메탄올-물, 에탄올-물, 아세톤-물 및 아세토니트릴-물의 二成分 混合溶媒에서 鹽化페닐메탄술포닐의 加溶媒分解反應을 速度論的으로硏究하였다. 反應速度는 反陽性子溶媒에서 보다 陽性子溶媒에서 더 빨랐으며, 이온化能力에 對한 反應速度의 感度 즉 Winstein 圖示의 m와 轉移狀態의 溶媒和數는 陽性子溶媒에서 훨씬 작았다. 이것은 陽性子溶媒의 水素結合溶媒和에 依한 初期狀態의 安定化로서 생각할 수 있다. 反應은 모든 溶媒系에 있어서 轉移狀態의 結合形成이 結合破壤을 앞지르는$S_N2$ 메카니즘으로 일어난다 할 수 있다.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.149-157
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• 2003

The purpose of this paper is to quantitatively investigate aging state of epoxy coating on containment structure at nuclear power plant. In order to evaluate an physical bonding of the epoxy coating, adhesion test was performed on a degraded epoxy coating on concrete specimens fabricated by accelerated aging experiment. In addition, impedance data by ultrasonic test were measured to compare with adhesion data. From almost 50 % of the specimens, aging phenomena of epoxy coating such as pin hole, blistering was discovered. To improve reliability on quality degradation of epoxy, co-relation between two kinds of different data was analyzed. By tracing co-related these data, it was possible to figure out physical state of as-built epoxy coating. The possibility to develop new methodology of time - dependent aging state on epoxy coating was found and discussed.