• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.260-264
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• 1996

In this study, the dieiectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability . As a result. first of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature, and the breakdown strength of specimens because it is believed that the adding filler farms interface and charge is accumulated in it, therefore the molecular motility is raised, the electric field is concentrated, and the acceleration of electron and the growth of electron avalanche are early accomplished. In the case of filled specimens with treating silane, the breakdown strength become much higher since the suggests that silane coupling agent improves interfacial combination and relays electric field concentration. Finally, from the analysis 7f weibull distribution. it was confirmed that as the allowed breakdown probability was given by 0.11[%].

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.120-129
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• 1994

A numerical investigation has been carried out for the electrochemical reaction, mass and heat transfer characteristics of the Molten Carbonate Fuel Cell(MCFC) stack. The effects of cooling air channel and water gas shift reaction were taken into account. The current density distribution of electrodes, the molecular fractions of reactant gasses and three dimensional temperature distribution can be calculated and shown by several lines of equivalent values. The results have been compared with the existing ones, and reasonable agreement has been obtained. To examine the influence of changing parameters, such as the composition of reactant gases, the target average current density, the utilization of reactant gases, the cooling air inlet temperature and flow rates, the computer simulation has been done. The analysis method and computer program developed in this study will be greatly helpful to design and verify the optimum operating condition of MCFC stack.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.52-52
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• 2002

Recently, nanoporous low-k materials using porogen (pore generating material) template method have gained much attraction due to the feasible advantage of dielectric constant decrease with the increase of porogen content, which is burning out and making air void by thermal curing. In nanoporous thin films, further, control of pore size and its distribution is very important to retain suitable thermal, mechanical and electrical properties. In this study, nanoporous low-k films were prepared with MTMS-BTMSE copolymer and porogen. The effect of interaction of copolymer matrix and porogen on pore size and distribution was comparatively to investigate with molecular structure and end functional group. The characterization of nanoporous thin film prepared was also performed using various techniques including NMR, GPC, Ellipsometer, FE-SEM, TGA, and FT-IR.

• Macromolecular Research
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• v.10 no.1
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• pp.18-23
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• 2002

We theoretically consider blends of two monodisperse one-end-functionalized homopolymers (denoted by A and B) capable of forming clusters between functional groups (stickers) using weak segregation theory. In this model system resulting molecular architectures via clustering resemble star copolymers having many A- and B-arms. Minimizing the total free energy with respect the cluster distribution, the equilibrium distribution of clusters is obtained and used for RPA (Random Phase Approximation) equations as input. For the case that polymers are functionalized by only one kind of sticker, the phase diagrams show that the associations promote the macrophase separation. When there is strong affinity between stickers belonging to the different polymer species, on the other hand, the phase diagram show a suppression of the macrophase separation at the range of high temperature regime, as well as the phase coexistence between a disordered and a mesoscopic phase at the relatively lower temperatures.

• Elastomers and Composites
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• v.34 no.4
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• pp.285-291
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• 1999

Effects of catalysts on network structure, hard segment length and distribution of polyurethane foams in the absence of catalysts were investigated. CFC free all MDI-based poly urethane foams were prepared from poly(ethylene adipate)glycol, 4,4'-diphenylmethane diisocyanate, and water. Amino catalysts used were 1,4-diazabicyclo[2,2,2]octane(DABCO), N, N,N',N'-tetramethyl--hexane-1,6-diamine(MR), bis(2-methylamino ethyl)ether(ET), 1,8-diazabicyclo-[5,4,0]-undecene-7(DBU). Dibutyltindilaurate(DBTL) as control was also used. Hard segment components of polyurethane foams were obtained by a selective degradation of polyester chains with 0.01N KOH-methanol solution. The PUFs with DBU catalyst contained more amount of isocyanurate components than other PUFs. On the other hand, the PUFs with ET, MR, DBTL catalysts contained more amount of allophanate and biuret component than the other PUFs.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.453-459
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• 2013

In phtosynthetic light harvesting complexes, the electronic transition energies of chlorophylls are influenced by the Coulombic interaction with nearby molecules. Variation of the interactions caused by structural inhomogeneity in biological environment results in a distribution of disordered electronic transition energies of chlorophylls. In order to provide a practical guide to predict qualitative tendency of such distribution, we model four porphyrin derivatives including chlorophyll a molecule interacting with an external positive charge and calculate their transition energies using the time dependent density functional method. It is found that ${\pi}-{\pi}^*$ transition energies of the molecules are generally blue-shifted by the charge because this stabilizes occupied molecular orbitals to a greater extent than unoccupied ones. Furthermore, new transitions in the visible region emerge as a result of the red-shift in energy of an unoccupied Mg orbital and it is suggested that light-induced electron transfer may occur from the tetrapyrrole ring to the central magnesium when the molecules are interacting with a positive charge.

• Macromolecular Research
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• v.8 no.4
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• pp.192-198
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• 2000

Cure characteristics and physical properties of carbon black-filled natural rubber (NR) compounds depending on the mixing procedure were studied using the compounds with different pre-final mixing (FM-1) stages. Carbon master batch (MB) and first and second remitting (1RM and 2RM) stages were employed as the FM-1 stage. Bound rubber content of the FM compound decreased with increasing the mixing steps. This was due to the decrease of the molecular weight distribution of the polymer by the rubber chain scission during the mixing. The Mooney viscosity decreased with increasing the mixing steps. Cure characteristics of the compounds were found to be different with the mixing procedures. The cure times of the compound became slower by increasing the number of the mixing steps. This was explained by the length of rubber chain, the carbon black network, distribution of the curatives in the compound, and immobilization of the polymeric segments. Modulus and tensile strength of the vulcanizate did not show a specific trend with the mixing procedure. Fatigue life of the vulcanizate increased by increasing the mixing stages.

• Nuclear Medicine and Molecular Imaging
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• v.41 no.2
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• pp.112-117
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• 2007

Imaging distribution of ${\beta}-amyloid$ plaques in Alzheimer's disease is very important for early and accurate diagnosis. Early trial of the ${\beta}-amyloid$ plaques includes using radiolabeled peptides which can be only applied for peripheral ${\beta}-amyloid$ plaques due to limited penetration through the blood brain barrier (BBB). Congo red or Chrysamine G derivatives were labeled with Tc-99m for imaging ${\beta}-amyloid$ plaques of Alzheimer patient's brain without success due to problem with BBB penetration. Thioflavin T derivatives gave breakthrough for ${\beta}-amyloid$ imaging in vivo, and a benzothiazole derivative [C-11]6-OH-BTA-1 brought a great success. Many other benzothiazole, benzoxazole, benzofuran, imidazopyridine, and styrylbenzene derivatives have been labeled with F-18 and I-123 to improve the imaging quality. However, [C-11]6-OH-BTA-1 still remains as the best. However, short half-life of C-11 is a limitation of wide distribution of this agent. So, it is still required to develop an Tc-99m, F-18 or I-123 labeled agent for ${\beta}-amyloid$ imaging agent.

• ALGAE
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• v.36 no.2
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• pp.111-121
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• 2021

Two cyanobacterial morphotypes isolated from Signy Island, South Orkney Islands, maritime Antarctica were characterised using a polyphasic approach combining morphological, cytological and molecular analyses. These analyses showed that the strains grouped with members of the genus Wilmottia. This genus currently includes three species, W. murrayi, W. stricta, and W. koreana. Both morphotypes analysed in this study were placed within the clade of W. murrayi. This clade showed a well-supported separation from Antarctic and New Zealand strains, as well as strains from other regions. W. murrayi was first described from Antarctica and is now known from several Antarctic regions. Confirmation of the occurrence of W. murrayi at Signy Island significantly extends its known distribution in Antarctica. In addition, a new combination, W. arthurensis, is suggested for Phormidium arthurensis.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.509-521
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• 2021

In this paper, from a review of the size distribution of the bubbles during pool scrubbing obtained from experiments by EPRI, we apply the bubble size distributions to analyses on the decontamination factors of pool scrubbing via I-COSTA (In-Containment Source Term Analysis). We perform sensitivity studies of the bubble size on the various mechanisms of deposition of aerosol particles in pool scrubbing. We also perform sensitivity studies on the size distributions of the bubbles depending on the diameters at the nozzle exit, the molecular weights of non-condensable gases in the carrier gases, and the steam fractions of the carrier gases. We then perform analyses of LACE-ESPANA experiments and compare the numerical ~ results to those from SPARC-90 and experimental results in order to show the effect of the bubble size distributions.