• Analytical Science and Technology
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• v.6 no.5
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• pp.479-487
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• 1993

Potassium-Graphite Fiber Intercalation Compounds(K-GFIC) have been prepared from well oriented pitch-based Graphite fiber by the transformed two-bulbs method with variation of reaction temperatures of graphite($T_g$ : $450^{\circ}C$, $400^{\circ}C$, $350^{\circ}C$, $300^{\circ}C$, $250^{\circ}C$). The stage transition process of K-GFICs was studied by X-ray diffraction methods, and we have observed peaks with d-values of (001) diffraction of $5.40{\AA}$ and $8.78({\pm}0.01){\AA}$, which are charecteristic for the stage 1 and stage 2, respectively. The stage stability and energy states of K-GFICs were studied by UV/VIS spectrophotometer. As a results, We found that the minimum values of reflactance of K-GFICs with pure stage was moved to higher energy pristine Graphite fiber's. But because of mixtured stage, we could not observe minimum reflectance in the visible region at high reaction temperatures($400^{\circ}C$, $450^{\circ}C$). From X-ray diffraction and UV/VIS sepctrophotometry data, we can suggest that K-GFICs with lower stage has many charge carriers existed between C atoms of graphite Layers. And then, these results also provides information on the electrical and other physical properties of K-GFICs.

• Journal of Yeungnam Medical Science
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• v.9 no.2
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• pp.224-238
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• 1992

Hepatic fibrosis was induced in Sprague-Dawley rats to evaluate the ultrastructural changes of fat-storing cells(Ito cells). For experimental induction of liver fibrosis, the rats were administered intraperitoneally with 0.5ml of 50% $Ccl_4$ solution per Kg body weight, twice weekly for 12 weeks. The rats were sacrified every week. The liver tissues were examined under light and eletron microscopes. And the immunohistochemical study of desmin was also performed. The results were summarized as follows : Light microscopic findings : The cellular infiltrations with inflammatory cells and Kupffer cells developed from 1 week after $Ccl_4$ injection, and were the most severe in 4 weeks. The strong immunoreactivity for desmin was also evident in 4 weeks. The centrilobular necrosis and fibrosis developed from 2 weeks after injection, and the necrosis persisted until 8 weeks. The progress of fibrosis was accompanied by decreases in cellular infiltration and reactivity for desmin, and increased gradual nodular formation was also observed. The cirrhosis was developed after 10 weeks. Electron microscopic findings : An increase in number of fat-storing cells was observed from 1 week after injection. Transitional cells characterized by a depletion of lipid droplets and a hypertrophy of the rER appeared after 2 weeks. The number of transitional cells with abundant collagen fibers in the extracellular spaces increased in 4 weeks. With progression of fibrosis the number of fat-storing cells decreased and proliferating fibroblasts with dilated rER were observed. According to these results it was revealed that there was an apparent transition from fat-storing cells to transitional cells and to fibroblasts. These cells had a few similar characteristics and may belong to the same cell population. Thus it was suggested that fat-storing cells might play an important role in hepatic fibrosis.

• Journal of the Korean Chemical Society
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• v.23 no.4
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• pp.243-247
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• 1979

Kinetics of the reaction of phenethyltosylate with substituted pyridines at 50, 60 and 70$^{\circ}C$ in acetonitrile were investigated by an electric conductivity method. The effects of substituents on the reaction of phenethyltosylate with pyridines were discussed. The rates of reaction were increased with electron donating power of substituents of pyridines. The isokinetic relationship was shown $E_{\alpha}$ and ${\Delta}S^{\neq}$, it's temperature was 240$^{\circ}$K. Bronsted plots were excellent linear except for 4-amino pyridine given by the following equation, logk=O. 22pKa-3.71 (r=O. 986). According to a plot of log k against Hammett substituent constants, the Iinearity was good except for bamino pyridine too, log k= -1.330${\sigma}$+0.08 (r= -0.987). In both cases, deviation of 4-amino pyridine from linearity was considered to solvent effect, resonance effect and ${\sigma}$ value itself. From all the above results, this reaction was found typical $S_N2$ reaction which the rates of reaction was determined by C…N bond formation at transition state.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.454-462
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• 1997

Thermotropic block copolyester(TLCP-b-PBN) based on poly(tetramethylene 2,6-(naphthaloyldioxy)dibenzoates)(TLCP) and poly(butylene 2,6-naphthalate)(PBN) was synthesized by solution polycondensation and melt-blended with poly(ethylene 2,6-naphthalate)(PEN) for in-situ composites. The TLCP domains showed nematic behavior in melt. The composition of block copolymer was determined from $^1H-NMR$ spectroscopy. The DSC thermogram of block copolymer revealed the presence of two major melting transitions, corresponding to the separete melting of PBN and TLCP domains. The glass transition temperature(Tg) of the PEN in the blends decreased with increasing the content of TLCP-b-PBN and the TLCP-b-PBN acted as a nucleating agent for the matrix polymers. In the 20% TLCP-b-PBN blend, well oriented TLCP fibriles were observed at temperature above the melting point of the PEN by optical microscopy. By scanning electron micrographs of cryogenically fractured surfaces of extruded blends, the TLCp domains were found to be finely and uniformely dispersed in 0.15 to $0.2{\mu}m$ size. Interfacial adhesion between the TLCP and matrix polymer was seemed to be good. Under certain condition TLCP formed a fiver structure in the PEN matrix, with thin oriented TLCP fibril in the skin region and spherical TLCP domains in the core.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.3 no.1
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• pp.18-25
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• 1978

The 1/f noise spectrum of short-circuited output drain current due to the Shockley-Read-Hal] recombination centers with a single lifetime in homogeneous nondegenerate MOS-field effcte transtors with n-type channel is calculated under the assumptions that the quasi-Fermi level for the carriers in each energy band can not be defined if we include the fluctuation for time varying quantities. and so 1/f noise is a majority carrier effect. Under these assumptions the derived 1/f noise in this paper show some essential features of the 1/f noise in MOS-field effect transistors. That is, it has no lowfrequency plateau and is proportionnal to the channel cross area A and to the driain bias voltage Vd and inversely proportional to the channel length L3 in MOS field effect transistors. This model can explain the discrepancy between the transition frequency of the noise spectrum from 1/f- response to 1/f2 and the frequency corresponding to the relaxation time related to the surface centers in p-n junction diodes. In this paper the results show that the functional form of noise spectrum is greatly influenced by the functional forms of the electron capture probability cn (E) and the relaxation time r (E) for scattering and the case of lattice scattering show to be responsible for the 4 noise in MOS fold effect transistors. So we canconclude that the source of 1/f noise is due to lattice scattering.

• Journal of the Korean Society of Radiology
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• v.8 no.7
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• pp.455-459
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• 2014

We grew the $Li_6Gd(BO_3)_3:Ce^{3+}$ scintillator and determined the scintillation and thermoluminescence properties for X-rays. The emission spectrum of $Li_6Gd(BO_3)_3:Ce^{3+}$ is located in the range of 370~500 nm, peaking at 423 nm an 455 nm, due to the $4f{\rightarrow}5d$ transition of $Ce^{3+}$ ions. The fluorescence decay time of the crystal is composed three components. The fast component is 60 ns (25%), the intermediate component is 787 ns (29%) and the slow component is $5.9{\mu}s$ (46%) of the crystal. The after-glow is caused by the electron and hole traps in the crystal lattice. We determined physical parameters of the traps in the crystal. The thermoluminescence trap are composed two traps. The determined activation energy (E), kinetic order (m) and frequency factor (s) of the first trap are 0.65 eV, 1.01 and $6.9{\times}10^8s^{-1}$. And, the determined activation energy, kinetic order and frequency factor of the second trap are 0.96 eV, 1.79 and $3.1{\times}10^{12 }s^{-1}$, respectively.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.5
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• pp.681-688
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• 1996

To investigate the effort of drying methods on the physicochemical properties of agar, gel strength, viscosity, melting and setting point, and phase transition by differential scanning calorimetery (DSC) during its heating were determined. In addition the structural differences of agar powder by scanning electron microscope (SEM) was examined. The most shortest onset temperature of gel strength increase was extruding method among any other methods. Viscosity of agar with hot air method, 400.00 cps at $45^{\circ}C$, was markedly increased, but with spraying and extruding ones were little change. The melting and setting point, and the temperature for maximum endothermic and enthalpy for agar with extruding one, $80.01^{\circ}C,\;36.05^{\circ}C\;and\;61.72^{\circ}C,\;0.73\;cal/g$, respectively, were lowest among the drying ones. But in the case of reheating after gelling, there were little change in all methods. Observing the surface structure of agar with SEM, extruding method showed the most unstable with absorptive property.

• Membrane Journal
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• v.21 no.3
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• pp.222-228
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• 2011

Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer was synthesized via atom transfer radical polymerization (ATRP) and used as an electrolyte for electrochromic device. Plasticized polymer electrolytes were prepared by the introduction of propylene carbonate (PC)/ethylene carbonate (EC) mixture as a plasticizer. The effect of salt was systematically investigated using lithium tetrafluoroborate ($LiBF_4$), lithium perchlorate ($LiClO_4$), lithium iodide (LiI) and lithium bistrifluoromethanesulfonimide (LiTFSI). Wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) measurements showed that the structure and glass transition temperature ($T_g$) of polymer electrolytes were changed due to the coordinative interactions between the ether oxygens of POEM and the lithium salts, as supported by FT-IR spectroscopy. Transmission electron microscopy (TEM) showed that the microphase-separated structure of PVC-g-POEM was not greatly disrupted by the introduction of PC/EC and lithium salt. The plasticized polymer electrolyte was applied to the electrochromic device employing poly(3-hexylthiophene) (P3HT) conducting polymer.

• Journal of the Korean Vacuum Society
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• v.2 no.2
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• pp.227-235
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• 1993

$SbS_{1-x}Se_xI,\;BiS_{1-x}Se_xI,\;Sb_{1-x}Bi_xSI,\;Sb_{1-x}Bi_xSeI,\;SbS_{1-x}Se_xI:Co,\;BiS_{1-x}Se_xI:Co,\;Sb_{1-x}Bi_xSI:Co$, and $Sb_{1-x}Bi_xSeI:Co$ single crystals were grown by the vertical Bridgman method using the ingots. It has been found that these single crystals have an orthorhombic structure and indirect optical transition. The composition dependences of energy gaps are given by $E_g(x)=E_g(0)-Ax+Bx^2$. The impurity optical absorption peaks due to cobalt deped with impurity are attributed to the electron transitions between the split energy levels of $Co^{2+}$ and $Co^{3+}$ ions sited at $T_d$symmetry of the host lattice.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.77-83
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• 2007

It is essential that second order nonlinear optical materials have low optical propagation losses in the wavelengths of second harmonic generation for practical applications in waveguides. Three dipolar chromophores substituted with nitro, cyano, and alkyl sulfone as an electron withdrawing group were prepared. The UV-Vis absorption spectra of the cyano and alkylsulfone chromophores showed a blue-shift compared to the nitro chromophore. The introduction of oxadiazole segment in the chromophore structure led to similar spectral shift. The blue-shift can produce low optical loses at second harmonics. The chromophores were successfully attached to a polyimide, yielding side chain polymers. The nonlinear optical property of the prepared optical polymers was determined by measuring electro-optic coefficient at 1.55 mm. The polymers exhibited high glass transition temperature of over $185^{\circ}C$ and thermal stability to $300^{\circ}C$ through differential scanning calorimeter analysis and thermal gravimetric analysis.