• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.783-792
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• 1995

Sol-Gel derived ferroelectric PZT thin films were fabricated on ITO/Glass and Si/SiO2 substrates. In order to investigate the effect of catalysts on the densification and crystallization of PZT thin films, a nitric acid or ammonium hydroxide was added to the PZT stock solution at the state of partial hydrolysis reaction. The measured pH for a stable PZT sol was 5.2~9.3. In case of an acid-catalyzed PZT sol, a highly condensed particulate PZT sol was formed by accelerating the hydrolysis reaction. But weakly branched polymeric PZT sol was formed with a base-catalyzed condition. The difference in densification behavior was not found in the pH range of added catalyst, but the refractive index of PZT thin film was increased rapidly as the annealing temperature increased. The PZT thin film annealed at 54$0^{\circ}C$ for 10 min was fully densified and its refractive index was above 2.4. When the annealing temperature increased, the transition from the pyrochlore phase to perovskite appeared at 54$0^{\circ}C$. The base-catalyzed PZT thin film suppressed to form the pyrochlore phase and proceeded effectively to convert the perovskite phase. This was due to the formation of polymeric molecular structure by controlling the hydrolysis and condensation reaction through the additiion of the ammonium hydroxide.

• Archives of Pharmacal Research
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• v.22 no.6
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• pp.585-591
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• 1999

The linker which plays a role in connecting a polymer with a scaffold has become an important part n solid-phase reaction. To develop a new linker for alcohols and carbohydrates, dihydropyran moiety was selected in this study. New linker, 1-($4^{l},5^{l}$-dihydro-5H-pyranyl)-7-hydroxyheptan-3-one (5) was synthesized via four steps from $\delta$-valerolactone. This can be called as DDHP-linked Wang resin due to double dihy-dropyran rings. To the one pyran ring of new linker 5 was added Wang resin and other alcohols and carbohydrates as scaffolds were then added successfully to the another pyran ring. Carbohydrate and hydroxyl resins were connected via new linker in a 70% loading yield. The detachment of glucose moiety in the presence of PPTS (2 equiv.) in 1:1 n-buteanol/1,2-dichloroethane at $60^{\circ}C$ for 12 h was carried out quantitatively. When certain combinatorial chemical works are carried out using this dihydropyran linker, Wang resin itself can be recovered. Its fact is particularly very important in industry, because recovered resins can be recycled.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.927-933
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• 1998

Polycrystalline powder of vanadium-doped forsterite (Vδ $Mg_2SiO_4$) was synthesized by the $H_2O_2$-assisted sol-gel method. The vanadium dopant, which was added as VO$(OMe)_3$ in methanol, went through several redox reactions as the sol-gel reaction proceeded. Upon adding VO$(OMe)_3$ to a mixture of $Mg(OMe)_2$ and Si$(OEt)_4$ in methanol, V(V) reduced to V(IV). As hydrolysis reaction proceeded, the V(IV) oxidized all back to V(V). Apparently, some of the V(V) reduced to V(IV) during subsequent gelation by condensation reaction. The V(IV) remained even after heat treatment of the gel in highly oxidizing atmosphere. The crystallization of the xerogel around 880 ℃ readily produced single phase forsterite without any minor phase. Using the polycrystalline powder as feeding stock, single crystals of vanadium-doped forsterite were grown by the floating zone method in oxidizing or reducing atmosphere. The doping was limited in low level because of the high partitioning of the vanadium in liquid phase during melting. The greenish single crystal absorbed visible light of 700∼1100 nm. But, no emission was obtained in near infrared range.

• PNF and Movement
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• v.20 no.1
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• pp.59-66
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• 2022

Purpose: The aim of this research was to verify the relationship between three-dimensional (3D) ground reaction force (GRF) and severity of leg length discrepancy (LLD) while walking at a normal speed. It used a 3D motion analysis system with force platforms in standing workers with LLD. Methods: Subjects comprising 45 standing workers with LLD were selected. Two force platforms were used to acquire 3D GRF data based on a motion analysis system during gait. Vicon Nexus and Visual3D v6 Professional software were used to analyze kinetic GRF data. The subjects were asked to walk on a walkway with 40 infrared reflective markers attached to their lower extremities to collect 3D GRF data. Results: The results indicated the maximal force in the posterior and lateral direction of the long limb occurring in the early stance phase during gait had significant positive correlation with LLD severity (r = 0.664~0.738, p <0.01). In addition, the maximal force medial direction of the long limb occurring in the late stance phase showed a highly positive correlation with the LLD measurement (r = 0.527, p <0.01). Conclusion: Our results indicate that greater measured LLD severity results in more plantar pressure occurring in the foot area during heel contact to loading response of the stance phase and the stance push-off period during gait.

• Bulletin of the Korean Chemical Society
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• v.27 no.6
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• pp.857-862
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• 2006

The catalytic enantioselective Michael reaction promoted by quaternary ammonium salts from Cinchona alkaloids as a phase-transfer catalyst is described. Treatment of malonates with $\alpha$,$\beta$-unsaturated ketones under mild reaction conditions afforded the corresponding Michael adducts in good yields with good to moderate enantiomeric excesses.

• Journal of Radiopharmaceuticals and Molecular Probes
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• v.3 no.2
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• pp.116-121
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• 2017

To overcome the low reactivity and solubility of alkali metal fluorides (MFs), various types of phase transfer catalysts (PTCs) have been developed over the last decades. However, since the fluoride activated by such PTC sometimes has a strong basicity, it may cause various side reactions such as elimination reaction or hydroxylation reaction in the nucleophilic fluorination reaction. Also, they may cause separation problems in the compound purification process. In recent advanced study, various PTCs have been developed to solve these problem of conventional catalyst. In this review, we would like to introduce three kinds of novel multifunctional organic catalysts such as bis-tert-alcohol-functionalized crown-6-calix[4]arene (BACCA), easy separable pyrene-tagged ionic liquid (PIL) by reduced graphene oxide (rGO), and tri-tert-butanolamine organic catalyst.

• Journal of the Korean Society of Combustion
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• v.7 no.3
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• pp.16-22
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• 2002

Combustion performance of an internally cycloned circulating fluidized bed for paper sludge was discussed through a series of batch type experiments. Operation parameters such as water content, feeding mass of sludge and secondary air injection rate were varied to find out the effect on the combustion performance, which was examined with carbon conversion rate and pollutant emission such as CO and NOx. A conventional solid fuel reaction was observed in the experiments of varying water content and feeding mass of the sludge, which is characterized with kinetic limited reaction zone, diffusion limited reaction zone and transition zone. Secondary air injection with swirl enhances the mixing of the gas phase as well as the solid phase, and improves combustion efficiency accompanied with higher carbon conversion rate and lower pollutant emission rate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.71-73
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• 1995

In this work, we synthsized GaN powders by the direct reactions of Ga with NH$_3$at the temperature range of 950∼1150$^{\circ}C$ and we growth the GaN thin films on Si and sapphire substrates using the synthesized GaN powders by the vapor phase epitaxy method. The synthesized powder had hexagonal crystal structures with lattice constants of a$\sub$0/=3.1895${\AA}$, c$\sub$0/=5.18394${\AA}$. The reaction rates of GaN were increased with both reaction time and temperature, however it did not depends on the flow rates of NH$_3$. The island type GaN crystals were grown on (0001) sapphire substrates and fast lateral growth of GaN on (111) Si substrate than sapphire was observed in our experiments.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.85-91
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• 2005

Effect of different cations to the formation of iron oxyhydroxide was studied using $M\ddot{o}ssbauer$ spectroscopy, X-ray diffraction (XRD) and BET. Redox Potential and pH were measured for the determination of the internal reaction rate, as well. The phases of iron oxyhydroxide could not be the same with each other, due to the presence of different cations in solution. Although the oxyhydroxide compound was composed of the same phases, the fraction of each phase was different from each other. The internal reaction rate was varied by the substitution of cation. It could be a cause of the different phase and particle size of oxyhydroxide compound.

• Journal of the Korean Applied Science and Technology
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• v.25 no.1
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• pp.48-51
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• 2008

Dipalmitoyl phosphatidyl choline and p-nitrophenyl palmitate were directly sonicated in acidic water for 6 minutes to give clear stock solutions. The catalytic hydrolysis of p-nitrophenyl palmitate was studied at $30-50^{\circ}C$ in the presence of unilamellar vesicle and mixture of unilamellar and multilamellar aggregates. The difference of reaction rate between unilamellar and multilamellar was observed. The rate of unilamellar reaction compared to the rate of mixture reaction showed more catalytic effect. The phase transition temperature of vesicle was measured at $37-44^{\circ}C$.