• Electrical & Electronic Materials
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• v.6 no.2
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• pp.175-183
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• 1993

Amorphous Semicondyctor로서 Chalcogenide계의 Ge-Se-Bi계 비정질화와 결정화 실험을 통하여 전기전도도를 평가코자 하였다. 시료의 조성범위는 G $e_{15-25}$S $e_{65-85}$B $i_{2.5-15B}$의 범위에서 5N의 Ge, Se, Bi metal분말을 사용하였다. 시료는 석영관에 진공 장입후 용융시켜 비정질화 하였다. 이때 열처리 조건은 1000.deg.C에서 10시간 동안 가열하였으며 급냉 조건은 3834.deg.C/sec로 처리하였다. 비정질 sample의 결정화는 결정핵을 형성 시킨 후 온도 변화 및 시간의 변화를 주면서 결정을 성장시켰으며 이때 B $i_{2}$S $e_{3}$와 GeS $e_{2}$ 결정상을 관찰 할 수 있었다. 박막화는 위의 실험에 사용된 Bulk sample을 사용하여 박막을 제작하였으며 유리화 영역은 Ge 15 at%, Se 70 at% 이상, Bi가 10 at% 이하일 때 비정질화가 용이하였다. Bulk의 경우 Ge를 20 at%로 고정시 Bi의 at% 함량이 증가함에 따라 전기전도도가 증가했으며 Bi가 7.5 at%이상일때 급격한 전도도의 증가를 가져왔다. 박막의 경우엔 Bulk sample보다 Bi의 함량이 증가시 더욱 큰 전도도의 증가를 가져왔다. G $e_{20}$S $e_{77.5}$B $i_{2.5}$ 저성의 결정화 경우 330.deg.C에서 4hr 유지시킨 경우가 가장 양호하였다.다.하였다.다.

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.611-618
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.6[mol%]Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere(N$_{2}$ gas). Metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100 [.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 106 [Hz], it move to low frequency with increasing resistivity of grain. The specimens showed three kinds of conduction mechanisms in the temperature range 25-125 [.deg. C] as the current increased: the region I below 200 [V/cm] shows the ohmic conduction. The region rt between 200 [V/cm] and 2000 [V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000 [V/cm] is dominated by the tunneling effect.fect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2206-2222
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• 1995

In this study, the characteristics of the three-dimensional turbulence flow in a rotating square sectioned 90.deg. bend were investigated by numerical simulation. And a dimensionless number, Coriolis force ratio, primarily subjected to the feature of the flow in the rotating 90.deg. bend was obtained as a result of one-dimensional theory. In the simulation study, low Reynolds number ASM developed by Kim(1991) in the square sectioned 180.deg. bend flow was modified in order to consider the rotational effects in the testing flows. In the near wall region of low Reynolds number, four turbulence models were employed and compared in order to find the most appropriate model for the analysis of the rotating 90.deg. bend flow. By comparison of the results with the experimental data, it is shown that low Reynolds number Algebraic Stress Model with rotating terms reflects most correctly the rotational effects. As the results of this study, centrifugal forces associated with the curvature of the bend and Coriolis forces and centripetal forces associated with the rotation affect directly both the mean motion and the turbulent fluctuations. Their actions on the mean flow are to induce a secondary motion while their effects on turbulence are to modify the pressure strain.

• Bulletin of the Korean Mathematical Society
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• v.49 no.4
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• pp.875-883
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• 2012

Let $\mathbb{F}_q$ be a finite field with q elements and $\mathbb{F}_q((X^{-1}))$ be the field of all formal Laurent series with coefficients lying in $\mathbb{F}_q$. This paper concerns with the size of the set of points $x{\in}\mathbb{F}_q((X^{-1}))$ with their partial quotients $A_n(x)$ both lying in a given subset $\mathbb{B}$ of polynomials in $\mathbb{F}_q[X]$ ($\mathbb{F}_q[X]$ denotes the ring of polynomials with coefficients in $\mathbb{F}_q$) and deg $A_n(x)$ tends to infinity at least with some given speed. Write $E_{\mathbb{B}}=\{x:A_n(x){\in}\mathbb{B},\;deg\;A_n(x){\rightarrow}{\infty}\;as\;n{\rightarrow}{\infty}\}$. It was shown in [8] that the Hausdorff dimension of $E_{\mathbb{B}}$ is inf{$s:{\sum}_{b{\in}\mathbb{B}}(q^{-2\;deg\;b})^s$ < ${\infty}$}. In this note, we will show that the above result is sharp. Moreover, we also attempt to give conditions under which the above dimensional formula still valid if we require the given speed of deg $A_n(x)$ tends to infinity.

• YAKHAK HOEJI
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• v.1 no.1
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• pp.2-4
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• 1948

Syringa oblata var dilatata (Nakai) Rehder is a oleaceous, deciduous shrub indigenous in the calcareous zones of Korea. The author researched the constituents of the leaves of the plant, especially the bitter principles which may be used as amara. According to the literature a bitter principle Syringin and Mannitol were isolated from the leaves of S. vulgaris L. And later on B. Power indicated that syringin and mannitol were widely distributed in oleaceous plants. The fresh leaves of the plant wer extracted with hot water, the filtered clear liquid was mixed with solution of lead acetate. The lead precipitate was filtered off and the filtered liquid was freed from lead by H$_{4}$S. The filtrate thus obtained was evaporated, and from the residue colorless needles, M. P. 166.deg., were obtained. It was soluble in water, in hot alcohol, and insoluble in ether and had a sweet taste. The results of the elementar analysis, M. P. and other characteristics agreed with that of d-mannitol. Finally it was proved to be identical with d-mannitol through conversion of it into Hexaacetyl mannitol, M. P. 124.deg., Triformal mannitol, M. P. 227.deg., Tribenzal mannitol, M. P. 224.deg., which exhibited no depression, when mixed with authentic specimens. The experiments to isolate bitter principles of the plant are in progress.

• Electrical & Electronic Materials
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• v.1 no.1
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• pp.54-61
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• 1988

This paper was a study on dielectric phenomena of the specimen, Polypropylene films which were annealled in air and quenched in liquid nitrogen after aging for 5[hr] in water of 100[.deg.C]. The specimen was measured in temperature range of 15-120[.deg.C] and in frequency range of 30-1x 10$^{6}$ [HZ]. As the results of the study, it was confirmed that the tacticity of specimen was isotactic structure, and the degree of cryatallinity of the specimens calculated by means of Natta's method from XRD (X-ray Diffraction) spectrum was 55[%]. And for dielectric relaxation, .betha. peak-the tan .delta. (spectrum around 20[.deg.C])-attributed due to amorphous regions, and .alpha. peak - the tan .delta. spectrum around 90[.deg.C]-due to crystalline regions. It was identified that the degree of crystallinity of the specimen quenched in the liquid nitrogen was increased to 55-65[%], and that of the specimen annealled in the air was decreased to 55-50[%]. And activation energy from dielectric loss spectra was obtained 34.5[kcal/mole] for .alpha. peak and 80.5[kcal/mole] for .betha. peak, respectively.

• Electrical & Electronic Materials
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• v.7 no.3
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• pp.187-199
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• 1994

In order to find an effect of structural changes due to variation of addition ratio of anhydride hardener and postcuring herat-treatments upon electrical properties of epoxy composites, the dielectric properties over a frequency range from 30[Hz] to l[MHz] were investigated in the temperature range of 20-180[.deg. C]. From the dielectric properties, the a peaks related with glass-transition phenomena of epoxy network appeared near 130[.deg. C], the conduction loss in high temperature region above 150[.deg. C] due to thermal dissociation of hardener started off with the low frequency side and the .betha. peak concerned with contribution of movable unreacted terminal epoxy groups and curing agents in the glass states concurred with the high-frequency side below 20[.deg. C]. And an effect of an hydride hardener upon structural changes and of postcuring heat treatments upon structural stability in epoxy composites would be explained through the estimation of the distribution of relaxation times and the activation energy for a .alpha. peak according to the WLF equations.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.98-109
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• 1995

An investigation was performed to study the inner damage of laminated composite plates subjected to out-of-plane load. During the investigation, inpact velocity and equivalent static load relationship was derived. Reddy's higher-order shear deformation theory(HSDT) and Hashin's failure criteria were used to determine inner stresses and damaged area. And impact testing was carried out on laminated composite plates by air gun type impact testing machine. The CFRP specimens were composed of [ .+-. 45 .deg. ]$_{4}$and [ .+-. 45 .deg. /0 .deg. /90 .deg. ]$_{2}$ stacking sequences with 0.75$^{t}$ * 26$^{w}$ * 100$^{l}$ (mm) dimension. After impact testing. As a result, a relationship holds between damaged area and impact energy, and a matrix cracking was caused by the interlaminar shear stress in the middle ply and was caused by the inplane transverse stress in the bottom ply.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1720-1725
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• 2015

The performance of the AlGaN/GaN MSM-2DEG varactor with different dielectric films deposited by the E-beam deposition is investigated in detail. The capacitance swing and the capacitance ratio of the varactor without dielectric film as well as with, SiO₂, Gd₂O₃, and Si₃N₄ films, respectively, are determined by electrodes of varying areas. The maximum capacitance, the minimum capacitance and the capacitance ratios are proportional to the increasing of the electrode areas. The capacitance ratio determined by the maximum and the minimum capacitance is found to be 18.35 (with Si₃N₄ dielectric film) and 149.51 (without dielectric film), respectively. The transition voltages of the fabricated varactors are almost the same for a bias voltage of about ±5 V and leakage current can be lower three orders of magnitude while the varactors with dielectric films. The tunability of the capacitance ratio makes the AlGaN/GaN MSM-2DEG varactor with a dielectric film highly useful in multirange applications of a surge free preamplier.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.12
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• pp.1610-1616
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$(0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere (N$_{2}$ gas). After being fired in a reducing atmosphere, metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100[.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. The results of the capacitance-valtage measurements indicated that the grain boundary was composed of the continuous insulating layers. The capacitance is almost unchanged below about 20[V], but decreased slowly over 20[V]. The conduction mechanism of the specimens observed in the temperature range of 25~125[.deg. C], and is divided into three regions having different mechanism as the current increased: the region I below 200[V/cm] shows the ohmic conduction. The region II between 200[V/cm] and 2000[V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000[V/cm] is dominated by the tunneling effect.ct.