• Journal of Magnetics
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• v.8 no.1
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• pp.1-6
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• 2003

The new class of $Gd_5(Si_xGe_{1-x})_4$ compounds undergoes a simultaneous magnetic/structural phase transition giving a high level of strain that can be induced either by change in temperature or by application of a magnetic field. Profound changes of structural, magnetic, and electronic changes occur in the $Gd_5(Si_xGe_{1-x})_4$ system lead to extreme behavior of the material such as the giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance. These unique material characters can be utilized for various applications including magnetic solid refrigerants, sensors, and actuators.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.216-217
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• 2006

A common problem in many fields of cryogenic power engineering is to apply high voltage to cold parts of superconducting equipment. In many of these cases a bushing provides electrical insulation for the conductor which makes the transition from ambient temperature to the cold environment. The cryogenic high voltage bushing for the 154kV, 100MVA high temperature superconducting(HTS) transformer is described. The bushing is energized with the line-to-ground voltage between the coaxial center and outer surrounding conductors, in the axial direction there is a temperature difference from ambient to about 77 K. For the insulation design of cryogenic bushing, the arrangement of condenser cone and electrical insulation characteristics of GFRP, Air, $LN_2$ and $GN_2$ were discussed in this paper.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.465-469
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• 2003

Microlens arrays were fabricated using a novel fabrication technology based on the exposure of a PMMA (Polymethylmethacrylate) sheet to deep X-rays and subsequent thermal treatment. X-ray irradiation causes the decrease of molecular weight of PMMA, which in turn decreases the glass transition temperature and consequently causes a net volume increase during the thermal cycle resulting in a swollen microlens. A new physical modeling and analyses for microlens formation were presented according to experimental procedure. A simple analysis based on the new model is found to be capable of predicting the shapes of microlens which depend on the thermal treatment. For the replication of microlens arrays having various diameters with different foci on the same surface, the hot embossing and the microinjection molding processes has been successfully utilized with a mold insert that is fabricated by Ni-electroplating based on a PMMA microstructure of microlenses. Fabricated microlenses showed good surface roughness with the order of 1 nm.

• Laser Solutions
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• v.11 no.3
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• pp.10-15
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• 2008

This study is aimed to analyse the laser glass bonding process numerically. Due to the viscoelastic behaviour of glass, the extremely large deformation of the frit seal is resulted continuously over the transition temperature, so that the thermal boundary condition be changed in the entire calculation process. The commercial FEM algorithm is restrictively able to remesh the large geometrical boundary shape and to adapt the boundary conditions simultaneously. According to our manual adaptation of increasing the laser line intensity to 700 mW/mm, it is possible to estimate the thermal glass bonding process under the fracture stress in principle. But it should be studied further in the case of high laser line intensity.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.896-897
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• 2006

In the viewpoint of engineering, materials problem is a key problem, which determines whether the exploitation of fusion energy will be success. The most important class of fusion materials is plasma-facing materials (PFM). W, as high Z high melting-point metal is one of the most important candidate materials due to its high plasma erosion resistance. Improving the ductility of W and W based alloy, lowering its ductile-brittleness transition temperature for meeting the requirements of fusion application is an important task. In this paper, severalpowder meatllurgy methods of fabricating W and W based materials are being investigated.

• Polymer(Korea)
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• v.30 no.6
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• pp.492-497
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• 2006

The epoxy composites are prepared with mixing temperature of epoxy/montmorillonite (MMT) melt master batch and the dielectric properties of the composites are also compared with intercalation of MMT. The exfoliation mainly occurrs iii the low content of MMT composites, while in the composites with high content of MMT the interspacing distance increases as the mixing temperature of epoxy/MMT master batch is increased. Class transition temperature of the composite which the MMT are effectively exfoliated is increased with the appropriate postcuring condition. Since the orientation polarization of dipoles in the epoxy molecules is restricted by the clay nanolayers exfoliated, the dielectric constant and dielectric loss of the composites are reduced. Furthermore, the dielectric properties could be improved by controling the mixing temperature and time of epoxy/MMT master batch as well as postcuring condition.

• Journal of Magnetics
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• v.4 no.1
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• pp.33-37
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• 1999

Unidirectional magnetic anisotropy field ($H_an$) was investigated for thin films of $CdCr{2-2x}In_{2X}Se_4 (0$\leq$x$\leq$0.2). This anisotropy originates from the microscopic anisotropic Dzyaloshinskii-Moriya (DM) interaction which arise from the spin-orbit scattering of the conduction electrons by the nonmagnetic impurities. This interaction maintains the remanent magnetization in the direction of the initial applied field. Then the single easy direction of the magnetization is parallel to the direction of the magnetic field. The anisotropy produced by field cooling is unidirectional I.e. the spins system deeps some memory of the cooling field direction. The chalcogenide spinel of$ CdCr_{2-2x}In){2X}Se_4$belongs to the class of the magnetic semiconductors. The magnetic disordered state is obtained when ferromagnetic structure is diluted by In. Then we have the mixed phase characterised by coexistence the magnetic long range ordering (IFN-infinite ferromagnetic network) and the spin glass order (Fc-finite clusters). The total magnetic anisotropy energy depends on the state of magnetic ordering. In our study we concentrated on the magnetic state with reentrant transition and spin glass state. The polycrystalline $ CdCr_{2-2x}In){2X}Se_4$ thin films were obtained by rf sputtering technique. We applied the ferromagnetic resonance (FMR) and M-H loop techniques for determining the temperature composition dependencies of Han. From the experimental data, we have found that Han decreases almost linearly when temperature is increased and in the low temperature is about three times bigger at SG state with comparison to the state with REE.

• Microbiology and Biotechnology Letters
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• v.51 no.3
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• pp.257-267
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• 2023

The potential polyhydroxyalkanoates (PHA)-producing bacteria, Bacillus megaterium PP-10, was successfully isolated and studied its feasibility for utilization of pineapple peel waste (PPW) as a cheap carbon substrate. The PPW was pretreated with 1% (v/v) H₂SO₄ under steam sterilization and about 26.4 g/l of total reducing sugar (TRS) in pineapple peel hydrolysate (PPH) was generated and main fermentable sugars were glucose and fructose. A maximum cell growth and PHA concentration of 3.63 ± 0.07 g/l and 1.98 ± 0.09 g/l (about 54.58 ± 2.39%DCW) were received in only 12 h when grown in PPH. Interestingly, PHA productivity and biomass yield (Y_x/s) in PPH was about 4 times and 1.5 times higher than in glucose. To achieve the highest DCW and PHA production, the optimal culture conditions e.g. carbon to nitrogen ratios of 40 mole/mole, incubation temperature at 35℃ and shaking speed of 200 rpm were performed and a maximum DCW up to 4.24 ± 0.04 g/l and PHA concentration of 2.68 ± 0.02 g/l (61% DCW) were obtained. The produced PHA was further examined its monomer composition and found to contain only 3-hydroxybutyrate (3HB). This finding corresponded with the presence of class IV PHA synthase gene. Finally, certain thermal properties of the produced PHA i.e. the melting temperature (T_m) and the glass transition temperature (T_g) were about 176℃ and -4℃, respectively whereas the M_w was about 1.07 KDa ; therefore, the newly isolated B. megaterium PP-10 is a promising bacterial candidate for the efficient conversion of low-cost PPH to PHA.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.629-632
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• 2013

Many properties of inorganic compounds are sensitive to changes in the point-defect concentrations. In minerals, such changes are influenced by temperature, pressure, and chemical impurities. Olivines form an important class of minerals and are magnesium-rich solid solutions consisting of the orthosilicates forsterite $Mg_2SiO_4$ and the fayalite $Fe_2SiO_4$. Orthosilicates have an orthorhombic crystal structure and exhibit anisotropic electronic and ionic transport properties. We examined the anisotropy of the electrical conductivity of $Fe_2SiO_4$ under the assumption that the electronic conduction in $Fe_2SiO_4$ occurs via a small polaron hopping mechanism. The anisotropic electrical conductivity is well explained by the electron transfer integrals obtained from the spin dimer analysis based on tight-binding calculations. The latter analysis is expected to provide insight into the anisotropic electrical conductivities of other magnetic insulators of transition metal oxides.

• Polymer(Korea)
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• v.29 no.4
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• pp.357-362
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• 2005

As a new class of electroluminescent (EL) polymers, PPV-based polymers containing sulfone group in the main chain were synthesized through Witting polymerization reaction to control n-conjugation length and energy levels for predictable light emission and enhanced device performance. These EL polymers showed good solubility in common organic solvents and high thermal stability with initial decomposition temperature of ca. $400^{circ}$ and glass transition temperature around $200^{circ}C$ Emission colors were tuned from green to deep blue by reducing ${\pi}$-conjugated length between sulfone groups. It was also noted from the cyclic voltammetry (CV) measurements and semiempirical calculations that sulfone group with high electron affinity effectively lowered HOMO-LUMO energy levels to enhance EL device performance.