• The Korean Journal of Ceramics
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• 제7권2호
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• pp.70-73
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• 2001

Phase transformation of TiSi$_2$ confined in sub-micron area of which the size is around or smaller than the grain size of C49 TiSi$_2$ phase is studied. It has been known that the C49 to C54 phase change is massive transformation that occurs abruptly starting from C54 nuclei located at triple point grain boundaries of C49 phase. When the C49 phase is confined in sub-micron area, however, the massive phase transformation is observed to be hindered due to the lack of the triple point grain boundaries of C49 phase. Heat treatment at higher temperatures starts to decompose the C49 phase, and the resulting decomposed Ti atoms diffuse to, and react with, the underneath Si material to form C54 phase that exhibits spherical interface with silicon. The newly formed C54 grains can also trigger the massive phase transformation to convert the remaining undecomposed C49 grains to C54 grains by serving as nuclei like conventional C54 nuclei located at triple point grain boundaries.

• 미생물학회지
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• 제30권1호
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• pp.65-69
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• 1992

It is proposed the polyacrylamide gel, instead of agar, could be used for the solid cultures of microorganisms including Streptomyces strains. Polymerization and gellation of 5% acrylamide solution were done by autoclaving for 5 min at 121.deg.C and no hindered by the addition of nutrient-rich media. In particular, pH buffer solution suitable for corresponding microorganisms must be used in the preparation of culture media. Comparing with agar, it was discussed that polycrylamide gel had many advantages such as gellation within the wide range of strong acid Carbon and Nitrogen sources, requirement tests of growth factors and minerals, sterization at high temperature, diffusion assays of products depending on the pore size of gel, and stability and standarization of microbial cultures.

• 한국표면공학회지
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• 제24권1호
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• pp.16-16
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• 1991

Generally brittle eta phase produced during TiC deposition has a effect on the TRS (transverse rupture strength ; thoughness). Therefore it is necessary to reduce eta(η), phase for the improvement of tool life. At this experiment some properties (TRS, bonding strength, tool life, eta phase)have been investigated by inserting TiN or TiCN underlayer between TiC layer and substrate. The results obtained were as follows; 1. by inserting underlayer eta phase were decreased and TRS was increased, but the bonding strength was decreased. 2. the diffusion of W, Co from the substrate was hindered by the underlayer. 3. TiC layer with TiCN underlayer had the finsest grain size. 4. by inserting underlayer (TiCN or TiN) the tool life was improved and especially notch and crater wear resistance was greatly improved.

• 한국표면공학회지
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• 제25권1호
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• pp.16-23
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• 1992

Generally brittle eta phase produced during TiC deposition has a bad effect on the TRS (transverse rupture strength ; thoughness). Therefore it is necessary to reduce eta(η) phase for the improvement of tool life. At this experiment some properties (TRS, bonding strength, tool life, eta phase) have been investigated by inserting TiN or TiCN underlayer between TiC layer and substrate. The results obtained were as fellows; 1. by inserting underlayer eta phase was decreased and TRS was increased, but the bonding strength was decreased. 2. the diffusion of W, Co from the substrate was hindered by the underlayer. 3. TiC layer with TiCN underlayer had the finsest gain size. 4. by inserting underlayer (TiCN or TiN) the tool life was improved and especially notch and crater wear resistance was greatly improved.

• Bulletin of the Korean Chemical Society
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• 제19권4호
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• pp.439-444
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• 1998

The protonation of tetraphenylporphyrin (TPP) in acidic organic solutions was analyzed by acid titrimetric and temperature-dependent absorption measurements. Competition between the protonation of free base TPP $(TPPH_2)$ and the solvation of proton by near solvent molecules determines the equilibrium of the diprotonated TPP $(TPPH_4^{2+})$ formation. The diprotonated TPP exists as an ion pair complex with the acid counterions, which are found to affect the degree of red shift of the Soret band. The rotation of the phenyl rings also plays an important role in the diprotonation, as suggested by the decrease in the degree of diprotonation for the fluorophenyl TPP derivatives whose phenyl ring rotation is significantly hindered relative to normal TPP. The difference of fluorescence lifetime between $TPPH_2 \;({\pi}_{FL}=19.6\;ns)\; and\; TPPH_4^{2+} \;({\pi}_{FL}=2.1 \;ns)$ was used advantageously to measure the rate of protonation in the excited state. The protonation of TPPH2 are found to occur much slower than the diffusion of protons from bulk solution to the porphyrin ring. The monoprotonated TPP is suggested to be the transient species for the diprotonation process.

• 공업화학
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• 제7권6호
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• pp.1043-1052
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• 1996

지방산의 분리방법중 증류나 추출 등의 전통적인 방법을 대체할 수 있는 공정으로 초임계유체 크로마토그래피 분리법을 추천할 수 있다. 그러나 지방산을 구성하는 탄소수나 불포화도는 초임계유체내에서 확산특성을 달리 하지만 이들의 정랑적인 데이터가 부족하여 초임계유체 크로마토그래피법을 공정화하는데 큰 어려움이 있다. 본 연구에서는 불포화도를 달리하는 지방산들의 초임계 이산화탄소내 확산계수를 CPB법(capillary peak-broadening method)을 기초로 온도 (308.15~328.15K)와 압력(13~17MPa)을 변수로 하여 실험적으로 측정하였다. 이성분계 확산계수는 일정한 온도에서 압력이 증가함에 따라 감소하며 일정한 압력에서 온도가 증가함에 따라 증가하였다. 일정한 밀도에서 온도에 따른 확산계수의 영향은 크지 않으며, 밀도와 점도가 증가함에 따라 확산계수는 감소하였다. 또한 Wilke-Chang식과 Funazukuri의 실험식, Matthews-Akgerman식을 초임계 이산화탄소에서의 이성분계 확산계수에 대한 상관식으로의 이용가능성을 확인한 결과 다른 상관관계식에 비해 RHS(rough hard sphere)에 기초한 자유부피모델인 Matthews-Akgerman식이 잘 일치하는 상관식인 것으로 확인되었다.

• Journal of Pharmaceutical Investigation
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• 제41권6호
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• pp.337-345
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• 2011

The objective of this work is to investigate the effect of chemical enhancer and current on the flux of donepezil hydrochloride (DH) through skin. Ethanol and N-methyl pyrrolidone (NMP) were used as chemical enhancers in combination with iontophoresis. We also have studied the effect of pH on flux and evaluated the role of electroosmosis. In vitro flux study was performed at $33^{\circ}C$, using side-by-side diffusion cell and full thickness hairless mouse skin. Passive flux of DH without enhancer was very small. As the concentration of enhancer increased, passive flux increased. After current application, flux increased markedly and the time to reach maximum decreased. Without enhancer, maximum flux was about 50 fold larger than that obtained without current. These results indicate that electromigration is playing a major role for the transport. As the enhancer concentration increased, flux also increased. NMP and ethanol increased not only the passive delivery, but also the iontophoretic delivery. Flux results indicate that ethanol has better ability than NMP in enhancing the transport of DH. The magnitudes of increase in flux by these enhancers indicate that there is a large synergistic effect in flux enhancement. Flux results from pH study showed that electroosmotic flow is reversed at low pH and the flux is hindered. These results provided some information on the flux enhancing ability of ethanol and NMP in combination with iontophoresis. The data also provided some mechanistic insights into the role of electromigration and electroosmosis on flux through skin.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.350-350
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• 2006

We investigated, via atomic force microscopy and transmission electron microscopy, the effect of shear force on the interfacial morphology of a reactive bilayer polymer system composed of PS-mCOOH and PMMAGMA. It has been observed that in the absence of oscillatory shearing the roughness of the interface increased with reaction period, while at large values of ${\gamma}_{0}\;and\;{\omega}$ it became less than that observed in the absence of oscillatory shearing. This observation may be attributable to the possibility that oscillatory shearing might have hindered the diffusion of polymer chains, which are located away from the interface, to the interface of the layers. However, the effect of ${\gamma}_{0}\;and\;{\omega}$ on the roughness of the interface of (PS-mCOOH)/(PMMA-GMA) bilayer is found to be quite different.

• 한국가시화정보학회지
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• 제3권1호
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• pp.3-19
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• 2005

Novel optical techniques are presented for three-dimensional tracking of nanoparticles; Optical Serial Sectioning Microscopy (OSSM) and Ratiometric Total Internal Reflection Fluorescent Microscopy (R-TIRFM). OSSM measures optically diffracted particle images, the so-called Point Spread Function (PSF), and dotermines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. The line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids. On the other hand, R-TIRFM is presented to experimentally examine the classic theory on the near-wall hindered Brownian diffusive motion. An evanescent wave field from the total internal reflection of a 488-nm bandwidth of an argon-ion laser is used to provide a thin illumination field of an order of a few hundred nanometers from the wall. The experimental results show good agreement with the lateral hindrance theory, but show discrepancies from the normal hindrance theory. It is conjectured that the discrepancies can be attributed to the additional hindering effects, including electrostatic and electro-osmotic interactions between the negatively charged tracer particles and the glass surface.

• Environmental Engineering Research
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• 제25권4호
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• pp.605-613
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• 2020

This study is to investigate the possibility of using activated carbon prepared from Iraqi date-pits (ADP) which are produced from palm trees (Phoenix dactylifera L.) as low-cost reactive material in the permeable reactive barrier (PRB) for treating lead (Pb⁺²) from the contaminated groundwater, and then compare the results experimentally with other common reactive materials such as commercial activated carbon (CAC), zeolite pellets (ZP). Factors influencing sorption such as contact time, initial pH of the solution, sorbent dosage, agitation speed, and initial lead concentration has been studied. Two isotherm models were used for the description of sorption data (Langmuir and Freundlich). The maximum lead sorption capacities were measured for ADP, CAC, and ZP and were found to be 24.5, 12.125, and 4.45 mg/g, respectively. The kinetic data were analyzed using various kinetic models particularly pseudo-first-order, pseudo-second-order, and intraparticle diffusion. COMSOL Multiphysics 3.5a depend on finite element procedure was applied to formulate transmit of lead (Pb⁺²) in the two-dimensional numerical (2D) model under an equilibrium condition. The numerical solution shows that the contaminant plume is hindered by PRB.