• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.117-120
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• 2007

This study deals with the free vibrations and buckling loads of column with clamped-spring ends and constant volume. The column has the regular polygon cross-section whose depth is varied with the linear functional fashion. The differential equation governing the free vibration of such column is derived in which the effect of axial load is included. The differential equation is solved numerically for calculating frequencies. By using the relationship between loads and frequencies, the buckling loads are also obtained.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.555-557
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• 2005

This paper proposed a hydraulic pump system that is driven by a variable SR drive. The operating pressure of hydric pump is limited by the pump speed and the mechanical structure. The operating of hydraulic pump is separated as constant pressure and constant flow region. Under fixed speed, the pressure can be controlled as constant value, and then decreased by increasing of pump speed. A 2.2[kW], 12/8-pole SR motor and DSP based digital controller are designed and tested for hydraulic pump system. The test results show that the system has some good features such as high efficiency and high response characteristics.

• 대한전기학회논문지
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• 제43권5호
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• pp.789-794
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• 1994

In this study, the structural and microwave dilelectric properties of 0.15BaO-0.15SmS12TOSI3T-0.7TiOS12T ceramics with sintering and annealing conditions were investigated. In the specimen sintered at 1350 [$^{\circ}C$], dielectric constant and quality factor were good values of 80.19,2006 (fS10T=4.6851[GHz]). To improve the $\tau$S1fT of specimen which was manufactured by the optimumsintering condition (1350[$^{\circ}C$],2[Hr.]), annealed from 2[hr.] to 16[hr.] at the annealing temperature of 1200 [$^{\circ}C$]. Increasing the annealing time, dielectric constant was almost constant and quality factor was increased. In the specimen of 4[hr.] annealed, the temperature coefficient of resonant frequency was minimum value, and increased with increasing the annealing time.

• 한국전기전자재료학회논문지
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• 제23권7호
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• pp.530-533
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• 2010

The proton exchange membrane fuel cell (PEMFC) holds great promise of clean power. However, in practical applications which use the PEMFC as the power source, the output voltage from the fuel cell undergoes a transient response especially during acceleration and deceleration. This paper presents the relationships between the charge curves of the internal voltage rise, discharge curves of the internal voltage drop, the voltage with a time constant $V_{\tau}$ and finally, the load and time constant $\tau$ of $FC_1$ and $FC_2$, connected both in series and in parallel.

• Bulletin of the Korean Chemical Society
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• 제22권7호
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• pp.732-738
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• 2001

The cross second-derivative of the activation energy,${\theta}$G${\neq}$ , with respect to the two component thermodynamic barriers, ${\theta}$G˚X and ${\theta}$G$^{\circ}C$Y, can be given in terms of a cross-interaction constant (CIC), $\betaXY(\rhoXY)$, and also in terms of the intrinsic barrier,${\theta}$G${\neq}$ , with a simple relationship between the two: $\betaXY$ = $-1}(6${\theta}$G${\neq}$).$ This equation shows that the distance between the two reactants in the adduct (TS, intermediate, or product) is inversely related to the intrinsic barrier. An important corollary is that the Ritchie N+ equation holds (for which $\betaXY$ = 0) for the reactions with high intrinsic barrier. Various experimental and theoretical examples are presented to show the validity of the relationship, and the mechanistic implications are discussed.

• 한국재료학회지
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• 제27권1호
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• pp.39-42
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• 2017

E-glass (electrical glass) fiber is the widely used as a reinforced composite material of PCBs (printed circuit boards). However, E-glass fiber is not stable because it has a dielectric constant of 6~7. On the other hand, D-glass (dielectric glass) fiber has a low dielectric constant of 3~4.5. Thus, it is adaptable for use as a reinforcing material of PCBs. In this study, we fabricated D-glass compositions with low dielectric constant, and measured the electrical and optical properties. In the glass composition, the boron content was changed from 9 to 31 wt%. To confirm the dependence of the dielectric constant on melting properties, D-glass with 22 wt% boron was melted at $1550^{\circ}C$ and $1650^{\circ}C$ for 2hrs. The glass melted at $1650^{\circ}C$ had a lower dielectric constant than the glass melted at $1550^{\circ}C$. Therefore, the D-glass with boron of 9~31 wt% was fabricated by melting at $1650^{\circ}C$ for 2hrs, and transparent clear glass was obtained. We identified the non-crystalline nature of the glass using an XRD (x-ray diffractometer) graph. The visible light transmittance values depending on the boron contents were measured and found to be 88.6 % ~ 82.5 %. Finally, the dielectric constant of the D-glass with 31 wt% boron was found to have decreased from 4.18 to 3.93.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 일렉트렛트 및 응용기술
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• pp.93-96
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• 2002

In this study, PZT thin films were fabricated using sol-gel processing onto Si/$SiO_2$/Ti/Pt substrates. PZT sol with different Zr/Ti ratio(20/80, 30/70, 40/60, 52/48) were prepared, respectively. The films were fabricated by using the spin-coating method on substrates. The films were heat treated at $450^{\circ}C$, $650^{\circ}C$ by rapid thermal annealing(RTA). The preferred orientation of the PZT thin films were observed by X-ray diffraction(XRD), and Scanning electron microscopy(SEM). All of the resulting PZT thin films were crystallized with perovskite phase. The fine crystallinity of the films were fabricated. Also, we found that the ferroelectric properties from the dielectric constant of the PZT thin films were over 600 degrees, P-E hysteresis constant. And the leakage current densities of films were lower than $10^{-8}A/cm^2$. It is concluded that the PZT thin films by sol-gel process to be convinced of application for ferroelectric memory device.

• 한국환경과학회지
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• 제13권1호
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• pp.37-40
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• 2004

In this study, the decomposition of gas-phase TCE, Benzene and Toluene, in air streams by direct UV Photolysis and UV/TiO$_2$ process was studied. For direct UV Photolysis, by regressing with computer calculation to the experimental results the value of reaction rate constant k of TCE, Toluene and Benzene in this work were determined to be 0.00392s$\^$-l/, 0.00230s$\^$-1/ and 0.00126s$\^$-1/, respectively. And the adsorption constant K of TCE, Toluene and Benzene in this work were determined to be 0.0519 mol$\^$-l/ ,0.0313mo1$\^$-1/ and 0.0084mo1$\^$-1/, respectively. For UV/TiO$_2$ system by regressing with computer calculation to the experimental results the value of reaction rate constant k of TCE, Toluene, and Benzene in this work were determined to be 5.74g/$\ell$$.$min, 3.85g/$\ell$$.$min, and 1.18g/$\ell$$.$min, respectively. And the catalyst adsorption constant K of TCE, Toluene, and Benzene in this work were determined to be 0.0005㎥/mg, 0.0043㎥/mg and 0.0048㎥/mg, respectively.

• 천문학회보
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• 제42권2호
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• pp.61.4-62
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• 2017

In this study we have made a statistical investigation on the kinematic classification of coronal mass ejections (CMEs) using about 4,000 SOHO/LASCO CMEs from 1996 to 2015. For this we use their SOHO/LASCO C3 data and exclude all poor events. Using the constant acceleration model, we classify these CMEs into three groups: Acceleration group, Constant Velocity group, and Deceleration group. For classification we adopt four different methods: Acceleration method, Velocity Variation method, Height Contribution method, and Visual Inspection method. Our major results are as follows. First, the fractions of three groups depend on the method used. Second, the results of the Height Contribution method are most consistent with those of the Visual Inspection method, which is thought to be most promising. Third, the fractions of different kinematic groups for the Height contribution method are: Acceleration (35%), Constant speed (47%), and Deceleration (18%). Fourth, the fraction strongly depend on CME speed; the fraction of Acceleration decreases from 0.6 to 0.05 with CME speed; the fraction of Constant increases from 0.3 to 0.7; the fraction of Deceleration increases from 0.1 to 0.3. Finally we present dozens of CMEs with non-constant accelerations. It is found that about 40 % of these CMEs show quasi-periodic oscillations.

• 품질경영학회지
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• 제25권1호
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• pp.80-99
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• 1997

This paper considers designing the simple (2-level) constant-and step-stress ALTs minimizing the asymptotic variance of the maximum likelihood estimator of the accelaeration factor, which is defined as the ratio of the 100qth percentile at use stress to that a specified stress, for items having lognormally-distributed lives. It is assumed that (i) the log-linear relationship exists between the stress and the mean log life, (ii) the standard deviation of the log life is constant, and (iii) the cumulative exposure model holds for the effect of changing stress. For the constant-stress ALT the low stress and the sample proportion allocated to low stress are determined and for two modes of stress loading of step-stress ALTs, the low-to-high and high-to-low, the low stress and the stress change time are determined. For selected values of the design parameters the optimum plans are figured, two modes of step-stress ALTs and the constant-stress ALT are compared to each other, and the effects of the incorrect pre-estimates of the design parameters are investigated.