• Macromolecular Research
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• v.12 no.4
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• pp.336-341
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• 2004

A new type of cross-linked methylaluminoxane (MAO)-supported cocatalyst has been prepared by the reaction of a soluble MAO and a cross-liking agent such as an aromatic diamine compound. The cross-linked MAO-supported cocatalyst was used for the polymerization of ethylene in the presence of bis(n-butylcyclopentadienyl) zirconium dichloride, (n-BuCp)$_2$ZrCl$_2$. The catalyst activity of (n-BuCp)$_2$ZrCl$_2$ cocatalyzed with the new supported cocatalyst was higher than that of the commercial silica-supported MAO (SMAO) cocatalyst. The molecular weight and the bulk density of the polyethylene produced by using the new supported cocatalyst were slightly higher than those of polyethylene synthesized using commercial SMAO. The resulting polyethylene particles possess spherical morphologies with very few fine particles.

• Macromolecular Research
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• v.16 no.4
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• pp.293-302
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• 2008

In our previous publication, the problem of particle deformation and coagulation at the nucleation stage in the presence of cross-linker was intensely studied by seeded batch dispersion polymerization of methyl methacrylate (MMA). In the present work, highly cross-linked, monodisperse PMMA particles were prepared under various reaction conditions by seeded semi-continuous process. Monodisperse, $6.5{\mu}m$-diameter PMMA particles containing up to 8 wt% of DVB or EGDMA were successfully made by seeded semi-continuous process and multi-semi-continuous addition process, respectively. Therefore, this study shows that seeded semi-continuous process is more effective and efficient to prepare highly cross-linked, monodisperse particles than non-seeded and seeded batch processes.

• Polymer(Korea)
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• v.24 no.3
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• pp.418-430
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• 2000

A new hydroxylpropyl chitosan (HPCTO) capable of forming both thermotropic and lyotropic liquid crystalline phases was synthesized by reaction of alkali chitosan with propylene oxide and its solid films cross-linked with glyoxal were prepared by casting the liquid crystalline solution in methanol. The thermal and swelling properties of the cross-linked films were investigated. The films displayed fingerprint patterns characteristic of cholesteric liquid-crystalline phase, and their pitches increased with increasing temperature and cross-linker concentration. The cross-linked samples exhibited an anisotropic swelling in both water and methanol, suggesting that the two-dimensional cross-linking preferentially performs between HPCTO molecules. The degree of anisotropy highly depended on the solvent, but hardly on the cross-linker concentration investigated.

• Asian-Australasian Journal of Animal Sciences
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• v.10 no.2
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• pp.245-250
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• 1997

Highly significant correlation (p < 0.001) was found between body weight and chest circumference of the local Katjang and cross-bred (local Katjang ♀ ${\times}$ German Fawn ♂ bucks under study. Increase in body length, chest circumference, depth of chest and height at withers (p < 0.001) reflected significantly the increase in body weight of the bucks. At the same age the cross-breds were bigger than the indigenous breed. No significant correlation was detected between body weight and scrotal circumference, or the latter with sperm counts in both buck types under study. However, the fluid portion of the semen increased in acidity and volume, the latter being significant (P < 0.01) in the local Katjangs, with increase in scrotal circumference. Although the effects of body condition on buck libido of both groups were not significant, the reaction time taken to mount the teaser females were significantly diminished (p < 0.001) with better body condition, at least in the local Katjangs. The reaction time gad an inverse, though not necessarily significant, relationship with semen characteristics such as volume, pH (in local Katjangs, p < 0.05), concentration, color (in cross-breds, p < 0.05), agglutination and mass movements in both phenotypes.

• Parasites, Hosts and Diseases
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• v.40 no.3
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• pp.113-117
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• 2002

We investigated the sero-prevalence of toxocariasis among healthy Korean adults in 1999. A total of 314 sera from normal inhabitants in Whachon-gun, Gangwon do, Korea was examined for specific antibody levels against excretory-secretory products of second stage larvae of Toxocara (TES). The presence of cross-reactions with other helminthiases such as cysticercosis, paragonimiasis, sparganosis or clonorchiasis was also checked by specific IgG ELISA. Sera showing positive reaction against TES were also tested by IgG immunoblot and by IgE ELISA. Out of 314 subjects, 16 was found to be positive by TES IgG ELISA and immunoblot, among whom 12 were also positive by TES IgE ELISA. Among the 16 seropositive samples, two sera showed positive reaction against Paragonimus and sparganum antigen, respectively. These results inferred that cross-reactions were negligible between toxocariasis and other helminthiases. Toxocariasis seroprevalence among Korean rural adults was detected to be approximately 5%.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1939-1944
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• 2011

The nucleophilic substitution reactions of bis(Y-aryl) chlorophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 35.0 $^{\circ}C$. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorophosphates (2). The substrate 1 has one more identical substituent Y compared to substrate 2. The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of cross-interaction constant (CIC) from negative ${\rho}_{XY}$ = -1.31 (2) to positive ${\rho}_{XY}$ = +1.91 (1), indicating the change of reaction mechanism from a concerted $S_N2$ (2) to a stepwise mechanism with a rate-limiting leaving group departure from the intermediate (1). The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines ($XC_6H_4ND_2$) show secondary inverse, $k_H/k_D$ = 0.61-0.87. The DKIEs invariably increase as substituent X changes from electron-donating to electron-withdrawing, while invariably decrease as substituent Y changes from electron-donating to electron-withdrawing. A stepwise mechanism with a rate-limiting bond breaking involving a predominant backside attack is proposed on the basis of positive sign of ${\rho}_{XY}$ and secondary inverse DKIEs.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.278-283
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• 1999

Formaldehyde has widely been used for the cross-linking of polyvinyl alcohol polyvinyl alcohol polymer. The effects of formaldehyde on the water resistance of MDF cement composites were investigated as a function of types of catalyst, base or acid, and the amount of formaldehyde. The acetalization, reaction of OH group of PVA with aldehyde, was ended incompletely under base atmosphere. However, by addition of citric acid, the cross-linking of PVA polymer could be acheved through acetalization of PVA and formaldehyde. The effects of these different patterne according to the types of catalyst on the water resistance of MDF cement were studied by the preparation of PVA films and MDF composites. Thanks to the cross-linking reaction of PVA polymer chains by formaldehyde, the modified PVA films and MDF composites showed a good water-resistant propety. The modified MDF cement composite to which 3 wt% formaldehyde and 1 wt% cirtic acid were added showed 80% of initial flexural strength and good interfacial state between cement grain and polymer matrix. However, 4 wt% formaldehyde deteriorted the processing conditions, microstructures and eventually the flexural strength, causing sharp increase in the viscosity of sample dough during the mixing process. To study the relatins of flexural strength and interface of cement grain and polymer matrix, SEM and MIP measurement were performed.

• Proceedings of the Korean Society of Life Science Conference
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• 2004.10a
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• pp.22-26
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• 2004

A self-replicating RNA ligase ribozyme was converted to a cross-catalytic format whereby two ribozymes direct each other's synthesis from a total of four component substrates. Each ribozyme binds two RNA substrates and catalyzes their ligation to form the opposing ribozyme. The two ribozymes are not perfectly complementary, as is the case for replicating nucleic acid genomes in biology. Rather, the ribozymes contain both template elements, which are complementary, and catalytic elements, which are identical. The specificity of the template interactions allows the cross-catalytic pathway to dominate over all other reaction pathways. In the presence of $2{\mu}M$ each of the corresponding substrates, one ribozyme catalyzes the synthesis of the second ribozyme with an initial rate of $6.8{\times}10^{-3}\;min^{-1}$, while the second ribozyme catalyzes the synthesis of the first with an initial rate of $2.9{\times}10^{-3}min{-1}$. As the concentration of the two ribozymes increases, the rate of formation of additional ribozyme molecules increases, consistent with the overall autocatalytic behavior of the reaction system. Here, I present results that possibly demonstrate a clue for a self-replicating molecule by showing an RNA ligase ribozyme, which is reminiscent of 'Prebiotic Era'.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2717-2724
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• 2020

Silicon, especially silicon in the form of SiO₂, is a major component of rocks. Final spent fuel storages, which are being designed, are located in suitable rock formations in the Earth's crust. Reduction of the uncertainty of silicon neutron scattering and capture is needed; improved silicon evaluations have been recently produced by the ORNL/IAEA collaboration within the INDEN project. This paper deals with the nuclear data validation of that evaluation performed at the LR-0 reactor by means of critical experiments and measurement of reaction rates. Large amounts of silicon were used both as pure crystalline silicon and SiO₂ sand. The critical moderator level was measured for various core configurations. Reaction rates were determined in the largest core configuration. Simulations of the experimental setup were performed using the MCNP6.2 code. The obtained results show the improvement in silicon cross-sections in the INDEN evaluations compared to existing evaluations in major libraries. The new Thermal Scattering Law for SiO₂ published in ENDF/B-VIII.0 additionally reduces the discrepancy between calculation and experiments. However, an unphysical peak is visible in the neutron spectrum in SiO₂ obtained by calculation with the new Thermal Scattering Law.

• Microbiology and Biotechnology Letters
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• v.10 no.3
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• pp.205-209
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• 1982

The enzyme-linked immunosorbent assay using the so-called "double-sandwich"technique was applied to determine Clostridium botulinum type F toxin. Polystyrene tubes were coated with horse anti-type F toxin serum and then toxin sample was added. The tubes were subsequently treated with rabbit anti-type F toxin IgG and sheep anti-rabbit serum IgG-horseradish peroxidase conjugate. By this technique, about 10 mouse intraperitoneal 50% lethal doses (ip LD/50/) of type F toxin could be detected. Low back-ground reading was achieved with the use of phosphate-buffered saline containing 0.05% Tween 20 and 1% bovine serum albumin as diluents of rabbit IgG and conjugate. Addition of EDTA in the diluents of toxin increased ELISA extinction value significantly. No cross-reaction was observed with botulinum type A and B toxin, but type E toxin gave sleight cross-reaction.