• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.9
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• pp.801-804
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• 2000

High-temperature superconductor of Bi-2212 system was fabricated by CFP(Centrifugal Forming Process). To make a uniform specimen slurry was prepared in the ratio of 7:3(powder : binder) and ball milled for 24 hours. Milled slurry was charged into a rotating mold with 450 rpm and dried at room temperature. Then the specimen was performed binder burn-out at 35$0^{\circ}C$ and heated for partial melting to 86$0^{\circ}C$. XRD analysis of most specimens were shown 2212 phase and observed a local plate shped microstructure with a well aligned c-axis direction from SEM images. Measured T$_{c}$(Critical temperature) was about 64 K.K.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.404-409
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• 1983

The warping of unsymmetric laminated composites is induced by residual curing stress at the room temperature. Classical lamination theory (C.L.T.) predicts the room temperature shapes of all unsymmetric laminates to be a saddle. Experimental observations, however, indicate some unsymmetric laminated composites have cylindrical room temperature shapes. This anomalous behavior is explained by the extention of C.L.T. which involves Von Karman's large deflection theory. It is shown that, depending on the thickness, width, length, curing temperature and room temperature of the laminate, critical boundaries of the shape change are determined. Theoretical predictions are compared with experimental results of Toray Graphite/Epoxy {O$_{n}$/90$_{n}$}$_{T}$./....

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.1-4
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• 2016

To observe the superconducting current and structural properties of high critical temperature ($T_c$) superconductors (HTS), we suggest the following imaging methods: Room temperature imaging (RTI) through thermal heating, low-temperature bolometric microscopy (LTBM) and Raman scattering imaging. RTI and LTBM images visualize thermal-electric voltages as different thermal gradients at room temperature (RT) and superconducting current dissipation at near-$T_c$, respectively. Using RTI, we can obtain structural information about the surface uniformity and positions of impurities. LTBM images show the flux flow in two dimensions as a function of the local critical currents. Raman imaging is transformed from Raman survey spectra in particular areas, and the Raman vibration modes can be combined. Raman imaging can quantify the vibration modes of the areas. Therefore, we demonstrate the spatial transport properties of superconducting materials by combining the results. In addition, this enables visualization of the effect of current flow on the distribution of impurities in a uniform superconducting crystalline material. These imaging methods facilitate direct examination of the local properties of superconducting materials and wires.

• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.824-832
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• 2008

micellar solution which is comprised of surfactant monomers, monodisperse micelles, and solvent(water) is studied from a statistical-mechanical point of view. The model examined in this article is for the ideal mixture of monomers, micelles, and solvent with the dielectric constant identical to that of solvent, which is an assumption common to continuum models. The model also reflects interactions between monomer and solvent molecule, and also between micelle and solvent molecule. The statistical-mechanical model under consideration yields ln $X_{CMC}=A+BT+C/T+D{\ln}T$ with $X_{CMC}$ being critical mcielle concentration (in mole fraction), being temperature, and A, B, C, D being constants which depend on the properties of the surfactant molecules. The statistical-mechanical model discussed in this article provides a theoretical basis on the thermal dependence of critical micelle concentration

• Journal of Surface Science and Engineering
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• v.31 no.6
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• pp.345-358
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• 1998

The evolution of surface roughness and morphology in epitaxial Si and $Si_{0.7}Ge{0.3}$ alloys grown by UHV opm-beam sputter deposition onto nominally-singular, [100]-, and [110]-mi-scut Si(001) was investigated by stomic force microscopy and trasmission electron microscopy. The evolution of surface roughness of epitaxial Si films grown at $300^{\circ}C$ is inconsistent with conventional scaling and hyperscaling laws for kineti roughening. Unstable growth leading to the formation of mounds separated by a well-defined length scale is observed on all substrates. Contraty to previous high-temperature growth results, the presence of steps during deposition at $300^{\circ}C$ increases the tendency toward unstable growth resulting in a much earlier development of mound structures and larger surface roughnesses on vicival substrates. Strain-induced surface roughening was found to dominate in $Si_{0.7}Ge{0.3}$ alloys grown on singular Si(001) substrates at $T_S\ge450^{\circ}C$ where the coherent islands are prererentially bounded along <100> directions and eshibt {105} facetting. Increasing the film thickness above critical values for strain relaxation leads to island coalescence and surface smoothening. At very low growth temperatures ($T_s\le 250^{\circ}C$), film surfaces roughen kinetically, due to limited adatom diffusiviry, but at far lower rates than in the higher-temperature strain-induced regime. There is an intermediate growth temperature range, however, over which alloy film surfaces remain extremely smooth even at thicknesses near critical values for strain relaxation.

• Progress in Superconductivity
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• v.6 no.1
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• pp.41-45
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• 2004

Polycrystalline Tl-1223 superconductors with a chemical composition of (Tl, Pb, Bi)TEX>$ (Sr, Ba)<_2$$Ca_2$$Cu_3$$O_{x}$ were synthesized by the solid state reaction method. The optimum chemical composition was $Tl_{0.8}$ $Pb_{0.2}$ $Bi_{0.2}$ $Sr_{1.8}$ $Ba_{0.2}$ $Ca_{2.2}$ $Cu_3$$O_{x}$ And the optimum sintering temperature and time were $905^{\circ}C$ and 7.5h, respectively. The sample was evaluated for their superconducting properties by magnetization measurement. The critical temperature $T_{c}$ is 120 K and the critical current density $J_{c}$ (T=5K, 0T) is estimated to be ∼ $10^{5}$ A/$\textrm{cm}^2$ for $Tl_{0.8}$ $Pb_{0.2}$ $Bi_{0.2}$ $Sr_{1.8}$ $Ba_{0.2}$ $Ca_{2.2}$$Cu_3$$O_{x}$ .

• Progress in Superconductivity and Cryogenics
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• v.26 no.1
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• pp.14-19
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• 2024

In this study, we explore the anisotropy of electron-phonon coupling (EPC) constant in epitaxially grown MgB₂ films on c-axis oriented Al₂O₃, examining its correlation with the critical temperature (T_c) and local structural disorder assessed through polarized Raman scattering. Analysis of the polarized Raman spectra reveals angle-dependent variations in the intensity of the phonon spectra. The Raman active mode originating from the boron plane, along with two additional phonon modes from the phonon density of states (PDOS) induced by lattice distortion, was distinctly observed. Persistent impurity scattering, likely attributed to oxygen diffusion, was noted at consistent frequencies across all measurement angles. The EPC values derived from the primary Raman active phonon do not significantly vary with changing observation angles, followed by that the T_c values calculated using the Allen and Dynes formula remain relatively constant across all polarization angles. Although the E_2g phonon mode plays a crucial role in the EPC mechanism, the determination of T_c values in MgB₂ involves not only electron-E_2g coupling but also contributions from other phonon modes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.550-553
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• 2001

In this study, unity current gain frequency f$\_$T/ of GaAs MESFET is predicted with different temperatures up to 400 $^{\circ}C$. Temperature dependence parameters of the device including intrinsic carrier concentration n$\_$i/ effective mass, depletion width are considered to be temperature dependent. Small signal parameters such as gate-source, gate dran capacitances C$\_$gs/ C$\_$gd/ are correlated with transconductance g$\_$m/ to predict the unity current gain frequency. The extrinsic capacitance which plays an important roles in high frequency region has been taken into consideration in evaluating total capacitance by using elliptic integral through the substrate. From the results, f$\_$T/ decreases as the temperature increases due to the increase of small signal capacitances and the mobility degradation. Finally the extrinsic elements of capacitances have been proved to be critical in deciding f$\_$T/ which are originated from the design rule of the device.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.16-19
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• 2013

The magneto-resistivity and electric field-current density (E-J) curves were investigated up to a magnetic field 9 T in the optimally doped $BaFe_{1.8}Co_{0.2}As_2$ single crystal with a superconducting temperature ($T_c$) of 24.6 K. The E-J Scaling behaviors below and above vortex glass transition temperature ($T_g$) were found, confirming the existence of the vortex glass phase transition. The critical exponents for the diverging spatial and time correlations at $T_g$, were obtained as v = $1.1{\pm}0.1$ and z = $4.5{\pm}0.3$, respectively. The obtained critical exponents are in good agreement with the predicted values of v ~ 1 - 2 and z > 4 within the 3D vortex glass theory.

• Journal of the Korean Chemical Society
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• v.47 no.1
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• pp.59-66
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• 2003

The comb-type grafted polymer hydrogels, which composed of N-isopropylacrylamide monomer and oligo(N-isopropylacrylamide-co-tert-butylacrylamide) [oligo(NIPAAm-co-t-BAM)], were synthesized by redox polymerization in 5~10% methanol aqueous solution using ammonium peroxodisulfate (APS) at 4 oC for 24h. The lower critical solution temperatures (LCSTs) of the comb-type grafted hydrogels were decreased with increase of t-BAM content in the grafted copolymer. We observed the effect of crosslinker and concentration of oligo(NIPAAm-co-t-BAM) on the shrinking/swelling ratio of hydrogels. Changes of shrinking/swelling ratio were decreased with increase of concentration of crosslinker. The increase of grafted oligo(NIPAAm-co-t-BAM) in the hydrogel shows an fast changes of shrinking/ swelling rate. The comb-type grafted hydrogels are expected to be valuable for the sensing materials of time-temperature labels(TTLs).