• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.54-54
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• 2018

To optimize the deposition parameters of diamond films, the temperature, pressure, and distance between the filament and the susceptor need to be considered. However, it is difficult to precisely measure and predict the filament and susceptor temperature in relation to the applied power in the hot filament chemical vapor deposition (HFCVD) system. In this study the temperature distribution inside the system was numerically calculated for the applied powers of 12, 14, 16 and 18 kW. The applied power needed to achieve the appropriate temperature at a constant pressure and other conditions was deduced, and applied to actual experimental depositions. The numerical simulation was conducted using the commercial computational fluent dynamics software, ANSYS-FLUENT. To account for radiative heat-transfer in the HFCVD reactor, the discrete ordinate (DO) model was used. The temperatures of the filament surface and the susceptor at different power levels were predicted to be 2512 ~ 2802 K, and 1076 ~ 1198 K, respectively. Based on the numerical calculations, experiments were performed. The simulated temperatures for the filament surface were in good agreement with experimental temperatures measured using a 2-color pyrometer. The results showed that the highest deposition rate and the lowest deposition of non-diamond was obtained at a power of 16 kW.

• 상하수도학회지
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• 제24권6호
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• pp.735-741
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• 2010

A pilot test was carried out to investigate the long term operation characteristics of Microfiltration (MF) system as a pretreatment for seawater reverse osmosis (SWRO) processes for two years. A commercialized MF module with pressurized operation type was used to filter seawater to remove particles which can foul reverse osmosis (RO) membrane. Silt Density Index (SDI) values of filtered seawater by the MF system were ranged from 0.14 to 1.79, which meet the SDI standard for RO feed water as depicted in previous literatures. Although the tested seawater is quite clean (i.e., dissolved organic cabon (DOC) concentration and turbidity were about 1 mg/l and less than 1 NTU, respectively) enough not to foul the MF membrane, steep increase in trans-membrane pressure (TMP) with a constant flux were observed over a whole operation period. A set of operation and water analysis data implies that the steep increase in TMP was resulted from iron and maganese fouling by the combination of metal corrosion by seawater and oxidation state by aeration and residual chlorine.

• 동력기계공학회지
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• 제17권6호
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• pp.47-53
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• 2013

The article focuses on the Temperature characteristics inside single loop oscillating heat pipe (OHPs). In this paper, heat pipe is experimentally studied thereby providing vital information on the parameter dependency of their thermal performance. The impact depiction has been done for the variation of tube model of the device. OHPs are made of copper capillary tubes of outer diameter 6.25 mm, inner diameter 4 mm heated by constant temperature water bath cooled by ambient temperature. Using four types of OHPs of copper capillary tubes length of 1500mm and HP length 650mm inside tubes working fluid is R-22 Pressure 8 bar and mass 34g,32g,28g,16g. The results indicate a strong influence of filling ratio on the performance.

• 에너지공학
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• 제2권3호
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• pp.308-314
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• 1993

15mbar 정합하에서 n.dodecane-1.decanol-1.dodecanol 혼합물의 삼성분계 및 각 이성분계의 기액평형 데이타와 비점을 측정하였다. 측정된 기액평형 데이타는 g$^{E}$ 모델식 인 Margules, van Laar, Wilson, NRTL, UNIQA 식에 의해 상관관계를 알아보았다. 이성분계 데이타는 Redlich-Kister의 적분법에 의해 열역학적으로 검토하였으며, 삼성분계 데이터 역시 McDermott-Ellis에 의한 two-point consistency test에 의해 질적으로 검토되었다. 이성분계의 기액평형 데이타 중에 n.dodecane-1.decanol계 만이 공비점을 보였다.

• Wind and Structures
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• 제26권6호
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• pp.355-367
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• 2018

This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D'Alembert's principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it's basically consistent about the divergence instability regularities in the flow separation model.

• Journal of Astronomy and Space Sciences
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• 제37권1호
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• pp.1-9
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• 2020

Frozen orbit is an attractive option for orbital design owing to its characteristics (its argument of pericenter and eccentricity are kept constant on an average). Solar sails are attractive solutions for massive and expensive missions. However, the solar radiation pressure effect represents an additional force on the solar sail that may greatly affect its orbital behavior in the long run. Thus, this force must be included as a perturbation force in the dynamical model for more accuracy. This study shows the calculations of initial conditions for a lunar solar sail frozen orbit. The disturbing function of the problem was developed to include the lunar gravitational field that is characterized by uneven mass distribution, third body perturbation, and the effect of solar radiation. An averaging technique was used to reduce the dynamical problem to a long period system. Lagrange planetary equations were utilized to formulate the rate of change of the argument of pericenter and eccentricity. Using the reduced system, frozen orbits for the Moon sail orbiter were constructed. The resulting frozen orbits are shown by two 3Dsurface (semi-major, eccentricity, inclination) figures. To simplify the analysis, we showed inclination-eccentricity contours for different values of semi-major axis, argument of pericenter, and values of sail lightness number.

• Transactions on Electrical and Electronic Materials
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• 제18권6호
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• pp.311-315
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• 2017

The perovskite system $(Ba^{2+}{_{1-x}}La^{3+}{_x})Fe^{3+}{_{1-t}}Fe^{4+}{_t}O_{3-y}$ (y = (1 - x --t)/2) having a composition of x = 0.0, 0.1, 0.2, and 0.3 showedean increase in $Fe^{4+}$ mole ratios with an increase in oxygen partial pressure ($N_2{\rightarrow}air{\rightarrow}O_2$), and with an increasefin s, the $Fe^{3+}$ quantity decreased and oxygen content (3-y value) increased. For each N sampls heat-treated in $N_2$ gas, a considerable weight gain, i.e.g a steadynincrease if oxygen content, was observed in the TGA data on the cooling process. The conductivity values at a constant temperature were in the order of $N_2$$O_2$; the respective log ${\sigma}$ values (${\Omega}^{-1}{\cdot}cm^{-1}$) at 323 K of the BL0 sample were -5.75 (BL0-N), -3.39 (BL0-A), and -0.53 (BL0-O). The mixed valencies of $Fe^{3+}$ and $Fe^{4+}$ ions in each sample were also confirmed by both the oxidation curve above 350 mV and the cathodic reduction curve below 200 mV from cyclic voltammetry.

• 동력기계공학회지
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• 제14권3호
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• pp.5-12
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• 2010

The purpose of this study is to analyze heterogeneous distribution of branch-like structure at downstream region of inner spray. The previous many studies about diesel spray structure have yet stayed in the analysis of 2-D structure, and there are very few of informations which are concerned with 3-D analysis of the structure. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray, and also the combustion characteristics of the diesel engines. Therefore, in order to investigate 3-D structure of evaporative spray the laser beam of 2-D plane was used in this study. Liquid fuel was injected from a single-hole nozzle (l/d=5) into a constant-volume vessel under high pressure and temperature in order to visualize the spray phenomena. The incident laser beam was offset on the central axis. From the images analysis taken by offset of laser beam, we examine formation mechanism of heterogeneous distribution by vortex flow at the downstream of the diesel spray. As the experimental results, the branch-like structure formed heterogeneous distribution of the droplets consists of high concentration of vapor phase in the periphery of droplets and spray tip of branch-like structure. Also the 3-D spatial structure of the evaporative diesel spray can be verified by images obtained from 2-D measurement methods.

• 열처리공학회지
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• 제1권1호
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• pp.1-7
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• 1988

In this study the improvement of mechanical properties of ion-nitrided SACM-1 steel was investigated by analysing microstructural developments and hardness increase in the nitrided surface layer. Specimens were quenched at $570^{\circ}C$, which is lower than the eutectoid temperature ($590^{\circ}C$) of Fe-N binary system after nitrided at temperature of $460-570^{\circ}C$ for 2-8 hours under constant pressure of 8 torr. The depths of diffusion and compound layers were appeared to proportional to the root mean square time of nitriding. And the hardness showed the maximun value Hv = 1200 for the specimen nitrided at $530^{\circ}C$. Hardness distribution of the. ion-nitrided steels were increased by diffusion treatment below the eutectoid temperature of the Fe-N binary system. A prolonged heat treatment below the eutectoid temperature was attributed to the increase in the depth of diffusion layer at the expense of the decrease in surface hardness of the ion nitreded steel.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.1066-1069
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• 2002

Dynamic postural control varies with the environmental context, specific task and intentions of the subject. In this paper, dynamic postural control against forward-backward perturbations of a platform was estimated using tri-axial accelerometers and a force plate. Ten young healthy volunteers stood upright in comfortable condition on the perturbation system which was controlled by an AC servo motor. With anterior-posterior perturbations, movements of ankle, knee and hip Joints were obtained by tri-axial accelerometers. and ground reaction forces with corresponding displacements of the center of pressure(CoP) by the force plate. The result showed that the ankle moved first and the trunk forward, which implies that the mechanism of the dynamic postural control in forward-backward perturbations, occurred in the procedure of the ankle, the knee and the hip. Knee flexion and hip extension in the period of acceleration, constant velocity and deceleration phase is very important fur the balance recovery. These responses depends on the magnitude and timing of the perturbation. From the present study the accelerometry-system appears to be a promising tool for understanding kinematic accelerative In response to a transient platform perturbation. A more through understanding of balance recovery mechanism may aid in designing methods for reducing falls and the resulting injuries.