• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.985-993
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• 1997

The effects of CaO and MgO fluxes on the fusibility of fly-ashes were investigated for two different fly-ashes. A fusion temperature of mixtures of selected fly-ashes and fluxes were measured by the ASTM test method(D1857) and the differential thermal analysis. IDT of these samples added CaO and MgO as a fluxing agent dropped in the range of 114 to $294^{\circ}C$ and 80 to $224^{\circ}C$, respectively. Compared with ash fusion temperature to Base/Acid ratio, the lowest ash fusion temperature were measured in the range of 0.7 to 0.8 for CaO-fly ash mixtures and 0.3 to 0.4 for MgO-fly ash mixtures. As a result, MgO in small addition acted as a more effective flux than CaO. A conventional Base/Acid ratio and liquidus point of ternary diagram did not show a good correlation with ash fusion temperature for these samples. In pure fusion temperature of fly ash-mixtures, DTA was better method than ASTM test method.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.260-260
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• 1999

We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

• Journal of Magnetics
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• v.16 no.1
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.745-750
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• 2000

YAG:Tb3+ as green phosphor were studied for the development of low voltage FED phosphor prepared by hydrothermal synthesis. We changed the concentration of luminescence center ion Tb3+ in hydrothermal reaction of which conditions were at 8M NH4OH as mineralizer, at 35$0^{\circ}C$ for 12hrs. As results, we could finally get the YAG:Tb3+ (Y3-xTbxAl5O12) powder of which particle size was about 0.2~1.0${\mu}{\textrm}{m}$. The excitation spectra and the green emitted spectra of YAG:Tb3+ phosphor powder were observed. When we doped 0.25 mol Tb to YAG, we could observe the maximum cathodoluminescence from YAG:Tb3+ phosphor and the chromaticity coordinate of the phosphor was shown x=0.35, y=0.56 in CIE1931 diagram.

• Progress in Superconductivity
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• v.3 no.1
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• pp.5-12
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• 2001

Our experimental research focuses on manipulating pinning deflects to alter the phase diagram of vortex matter, creating new vortex phases. Vortex matter offers a unique opportunity for creating and studying these novel phase transitions through precise control of thermal, pinning and elastic energies. The vortex melting transition in untwinned YB $a_2$C $u_3$ $O_{7-}$ $\delta$/ crystals is investigated in the presence of disorder induced by particle irradiation. We focus on the low disorder regime, where a glassy state and a lattice state can be realized in the same phase diagram. We follow the evolution of the first order vortex melting transition line into a continuous transition line as disorder is increased by irradiation. The transformation is marked by an upward shift in the lower critical point on the melting line. With columnar deflects induced by heavy ion irradiation, we find a second order Bose glass transition line separating the vortex liquid from a Bose glass below the lower critical point. Furthermore, we find an upper threshold of columnar defect concentration beyond which the lower critical point and the first order melting line disappear together. With point deflect clusters induced by proton irradiation, we find evidence for a continuous thermodynamic transition below the lower critical point..

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.3
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• pp.344-351
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• 1997

The experiment was conducted to examine the varietal variation in gelatinization of rice flour and adaptability to rice bread processing, and the interrelation among the relevant properties. IR 44 showed the lowest temperature of gelatinization onset(T$_{o}$ ) and the highest gelatinization enthalphy(ㅿH) measured by differential scanning calorimetry (DSC). The following lower T$_{o}$ was found with the order of Suweon 230＜Pusa-33-30＜T(N) 1, Daeribbyeo 1 and the next higher ㅿ.H was followed by the order of Pusa-33-30＞Suweon 230. IRAT 177 revealed the highest temperature of gelatinization onset and conclusion(T$_{c}$) and the following higher T$_{c}$ was found with the order of Pusa-33-30＞AC 27＞Nonganbyeo. The varietal range of T$_{o}$ and T$_{c}$ was 50.0~72.5$^{\circ}C$ and 70.2~87.4$^{\circ}C$, respectively. The rice materials tested can be classified by scatter diagram on the plane of upper two principal components contracted from DSC thermogram and various characteristics relevant to processing and sensory preference of rice bread by principal component analysis. AC27, Suweonjo and IR 44 among high-amylose rices showed better suitability to rice bread processing. The temperatures of gelatinization peak and conclusion of rice flour checked by DSC were significantly negatively associated with springiness of rice bread. The most properties relevant to processing and sensory preference of rice bread such as hardness, moistness, springiness, cohesiveness, specific loaf volume and distribution or size of air cell revealed the close correlation between each other.other.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.739-743
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• 2003

[ $Ba_2NaNb_5O_{15}$ ], hereafter BNN, thin films are attractive candidates for nonvolatile memory and electro-optic devices. In the present work, thin films that have different contents of Ba, Nb and Na have been prepared by H-MOD technique on silicon and Pt substrates. XRD and SEM were used to investigate the phase evolution behavior and the microstructure of the films. It was found that the films of about 500nm thick were crack-free and uniform in microstructure. Nb content strongly influenced the phase formation of the films, where unwanted phases were always formed at the stoichiometric BNN composition. However, the unwanted phases decreased with the increase of excess Nb content, and the single phase (tetragonal tungsten bronze structure) BNN thin film was obtained when the niobium content reached some point. From this study, the sub-solidus phase diagram below $850^{\circ}C$ for $BaO-Na_2O-Nb_2O_5$ ternary system is proposed.

• Progress in Superconductivity
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• v.4 no.2
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• pp.153-156
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• 2003

We have studied fabrication of $MgB_2$ thin film on $SrTiO_3$ (001) and r-cut $A1_2$$O_3$ substrates by rf magnetron sputtering method using and $ MgB_2$ single target and two targets of Mg and B, respectively. Based on P -T phase diagram of $MgB_2$ and vapor pressure curves of Mg and B, a three-step process was employed. B layer was deposited at the bottom to enhance the film adhesion to the substrate. Secondly, co-sputtering of Mg and B was done. Finally, Mg was sputtered on top to compensate fur the loss of Mg during annealing. Subsequently, $MgB_2$ films were in-situ annealed in various conditions. The sample fabricated using the three-step process showed $T_{c}$ of 24 K and formation of superconducting $MgB_2$ phase was confirmed by XRD spectra. In case of co-sputtering deposition, $T_{c}$ depended on annealing time and argon pressure. However, those made by single-target sputtering showed non-superconducting behavior or low transition temperature, at best.est.

• Journal of Astronomy and Space Sciences
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• v.20 no.4
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• pp.249-260
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• 2003

CCD photometric observations of a W UMa type contact binary AH Cnc were performed for ten nights from December 1998 to May 1999 using a PM512 CCD camera and BVI filters attached to the 61㎝ reflector at Sobaeksan Optical Astronomy Observatory. New BVI light curves were analyzed with contact Mode 3 of the Wilson-Devinney binary model. We obtained photometric solutions and Roche geometry of this binary system. Through the analysis of the (O-C) diagram with all times of minimum light published so far and including hour's secular variations of orbital period and the mass transfer rate were calculated.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.1029-1036
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• 2012

Push-pull-type copolymers - low-band-gap copolymers of electron-rich fused-ring units (such as cyclopentadithiophene; CPDT) and electron-deficient units (such as benzothiadiazole; BT) - are promising donor materials for organic solar cells. Following a design principles proposed in our previous study, we investigate the electronic structure of a series of new CPDTBT derivatives with various electron-withdrawing groups using the time-dependent density functional theory and predict their power conversion efficiency from a newlydeveloped protocol using the Scharber diagram. Significantly improved efficiencies are expected for derivatives with carbonyl [C=O], carbonothioyl [C=S], dicyano [$C(CN)_2$] and dicyanomethylene [C=$C(CN)_2$] groups, but these polymers with no long alkyl side chain attached to them are likely to be insoluble in most organic solvents and inapplicable to low-cost solution processes. We thus devise several approaches to attach alkyl side chains to these polymers while keeping their high efficiencies.