• Journal of Energy Engineering
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• v.23 no.4
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• pp.230-235
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• 2014

In this study, performances of the vane expander protype for micro organic Rankine cycle with refrigerant R134a as a working fluid have been analyzed. While operating organic Rankine cycle for analysing expander efficiencies such as overall efficiencies, volumetric efficiencies and mechanical efficiencies under $110^{\circ}C$ of expander inlet temperature, the power of the expander, inlet temperature of expander, inlet pressure of expander and the flow rate of the working fluid(refrigerant R134a) have been measured while varying the rotational speed of the expander. It was found that the more the expander revolution speed is high, the more the expander power, overall efficiencies and volumetric efficiencies are higher. In case of 500 rpm of rotational speed, overall efficiencies are 6~7% and in case of 1000 rpm, overall efficiencies are 11~12%. We have found that low volumetric efficiencies result in poor overall efficiencies.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.289-296
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• 2017

In this paper, geometrical optimization for newly designed flapping mechanism for insect-like micro air vehicle is presented. The mechanism uses strings to convert rotation of motor to reciprocating wing motion to reduce the total weight and inertial force. The governing algorithm of movement of the mechanism is established considering the characteristic of string that only tensile force can be acted by string, to optimize the kinematics. Modified pattern search method which is complemented to avoid converging into local optimum is adopted to the geometrical optimization of the mechanism. Then, prototype of the optimized geometry is produced and experimented to check the feasibility of the mechanism and the optimization method. The results from optimization and experiment shows good agreement in flapping amplitude and other wing kinematics. Further research will be conducted on dynamic analysis of the mechanism and detailed specification of the prototype.

• 프린팅코리아
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• v.7 no.8
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• pp.38-43
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• 2008

RFID(Radio Frequency Identification)는 IC칩과 무선을 통해 식품, 동물, 사물 등 다양한 개체의 정보를 관리할 수 있는 첨단 인식 기술이다. 기존에 널리 사용되고 있는 바코드가 일정한 방향으로 인쇄된 내용을 리더기를 이용해야만 인식하는데 비하면 RFID는 초소형칩(IC)을 내장해 무선 주파수로 추적하기 때문에 인식범위가 넓고 인식 속도 역시 매우 빠르다. 뿐만 아니라 담을 수 있는 정보량에서도 모델에 따른 차이는 있지만 바코드와는 비교가 되지 않을 정도로 많다.

• Journal of the Korean Chemical Society
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• v.23 no.4
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• pp.217-236
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• 1979

The author's theory for plastic deformation was applied to superplastic alloys (Zn-Al eutectoid, Al-Cu, Pb-Sn, Sn-Bi, Mg-Al eutectics). The plastic deformation of the superplastic alloys could be described by two Maxwell models connected in parallel which represent two grain boundary flow units. The flow units are characterized by the two parameters $X_{gj}/{\alpha}_{gj}\;and\;{\beta}_{gj}$ (j=l or 2, g signifies the grain boundary) the values of which were obtained by applying our flow equation [Eq. (5)] to experiment. We confirmed that our flow equation describes the superplasticity very well. The curve of strain rate sensitivity m (=${\partial}\;In\;f/{\partial}\;In\;\dot{s})\;vs.\;-In\dot{s}$, where f and s are stress and strain rate, respectively, showed two peaks corresponding to flow unit gl and g2, the separation of the two peaks is determined by the difference between ${\beta}_{g1}\;and\;{\beta}_{g2}$. The condition of superplasticity is also determined by ${\beta}_{gj}$, which satisfies $\dot{s}_{mj}{\leqslant}1.53}{\beta}_{gj}$ [Eq.(13)], where $\dot{s}_{mj}$ is the s of the jth unit at the peak. The grain size dependence of ${\beta}_{gj}$ is described by $ln({\beta}_{gj})^{-1}$=alnx+b [Eq. (16)], where x is the grain size, and a and b are constants. The activation enthalpy for each flow unit, ${\Delta}H_{gj}^{\neq}$ was also determined from the temperature dependence of ${\beta}_{gj}$ which is proportional to the relaxation time of the j th unit. Since the superplasticity is determined by Eq. (13), and since ${\beta}_{gj}$ and ${\Delta}H_{gj}^{\neq}$ are related, we obtained the conclusion that superplasticity occurs in the system having small ${\Delta}H_{gj}^{\neq}$ values. The Aej values were equal to the activation enthalpies of grain boundary self-diffusion of the component atoms of the alloys, this accords with our proposed flow mechanism. The ${\Delta}H_{gj}^{\neq}$ value increases with grain size as expected from Eq. (16).

• Journal of Aquaculture
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• v.21 no.2
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• pp.76-81
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• 2008

We investigated the food-effect for ultra-small rotifer Synchaeta kitina cultured under a individual and community by several diets: 3 single trials(Tetraselmis suecica, TET; Isochrysis galbana, ISO; Marine Chlorella ellipsoidea, CHL) and 3 trials with a mixture of 2 species. The rotifer was cultured on the different feeding concentrations. In the individual cultures, the maximum number of offsprings and maximum lifespan of the female investigated to 5.8 inds. and 12.7 days in TET trial, respectively. Values of the developmental phases of the rotifer fed with T. suecica were higher than those of trials without T. suecica. Also it approached faster to maturation level. In the community cultures, the maximum density of TET+CHL trial elevated up to 1,569 inds./mL. But, CHL and ISO showed a poor growth rate and maximum density. The offsprings of the female increased continuously when fed by T. suecica trial, up to $10{\times}10^3$ cells/ind./day. As the quantity of supplied diet was lowered their lifespan were decreased. But, the maximum density and growth rate in the community cultures showed the highest value in the $10{\times}10^3$ cells/ind./day. The efficient food for mass culture of S. kitina was T. suecica, and optimum concentration of their food was 10,000 cells for an individual.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.49-49
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• 1999

리튬 이차 전지를 박막화함으로써 개발된 고상의 마이크로 박막전지는 임의의 크기 및 형태로의 제작이 가능하며 액체전해질을 사용하지 않기 때문에 작동 중 열 또는 기체 생성물이 생기지 않아 높은 안정성을 갖으며 광범위한 사용 온도 범위를 가진다. 위와 같은 장점으로 인하여 충전 가능한 고상의 박막형 리튬 이차 전지는 점진적으로 그 사용 범위가 크게 확대될 것으로 판단된다. 즉, 초소형 전자, 전기 소자는 물론이며 조만간 실현될 스마트 카드, 셀루러폰 및 PCS와 같은 개인용 휴대 통신장비의 전력 공급계로의 응용이 가능할 것이다. 특히 장수명, 고에너지 밀도를 갖는 초소형의 전지를 필요로 하는 microelectronics, MEMS등에 이용될 수 있는 이차전지에 대한 요구가 점점 가시화 됨에 따라 박막공정을 이용한 이차전지개발기술이 요구되고 있으며, 박막제조기술을 이용한 고상의 박막형 및 전지에 관한 연구가 증가하고 있다. 본 연구에서는 박막형 리튬 이차전지의 Cathode 물질로써 비정질의 산화바나듐 박막을 반응성 스퍼터링에 의하여 상온에서 증착하였다. 박막형 이차전지의 여러 가지 Cathode 물질중 산화바나듐은 다른 물질들과는 달리 비정질 형태로 매우 우수한 충방전 특성을 나타낸다. 이런 특성으로 인해 다소 전지자체의 성능은 낮지만 저전력 저전압을 필요로 하는 초소형 전자 소자와 혼성되어 이용할 수 있는 잠재성이 매우 높은 물질이다. 바나듐 타겟의 경우 타겟 표면의 ageing에 따라 증착되는 박막의 특성이 매우 달라지게 되므로 presputtering의 시간을 변화시키면서 실험하였다. 또한 스퍼터링 중의 산소의 분압도 타겟의 ageing에 많은 영향을 주므로 실험 변수로 산소분압을 변화시키면서 실험하였다. 증착된 산화바나듐 박막의 표면은 scanning electron microscopy로 분석하였으며 구조 분석은 X-선 회절분석, X-ray photoelectron spectroscopy 그리고Auger electron spectroscope로 하였다. 증착된 산화바나듐 박막의 전기화학적 특성을 분석하기 위하여 리튬 메탈을 anode로 하고 EC:DMC=1:1, 1M LiPF6 액체 전해질을 사용한 Half-Cell를 구성하여 200회 이상의 정전류 충 방전 시험을 행하였다. Half-Cell test 결과 박막의 결정성과 표면상태에 따라 매우 다른 전지 특성을 나타내었다.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.89-97
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• 2021

STEP Cube Lab-II (Cube Laboratory for Space Technology Experimental Project-II) is a 6U Cube satellite equipped with optical and infrared cameras for monitoring Mt. Paektu volcanic eruption signs and earth observation in the Korean peninsula. To guarantee successful mission operation of the cube satellite in orbit, thermal design is essential for the electronic equipment, and must be kept within the allowable temperature range during the mission period. Thus, it is necessary to analyze the predictable orbital thermal environment. The STEP Cube Lab-II is launched through the KSLV-II, however, the operation orbit has not been determined due to the unknown launch time. In this study, we performed a thermal analysis of the satellite and investigated the heat flux according to launch time to analyze the worst orbital conditions that could occur.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.3
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• pp.489-496
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• 2019

In this paper, we design and fabricate an ultra small dual crossed dipole antenna operating at 2.4 GHz frequency. In order to miniaturize the size of the antenna so that it can be applied to a mobile device, a cross dipole is disposed on the upper two layers and a reflection plane, a horizontal matching circuit and a ground plane are arranged on each layer. The circuit was connected by a vertical through-hole. The size of the fabricated antenna is $21.61mm{\times}16.88mm{\times}1.27mm$, the measured reflection coefficient is -31.5 dB, and the bandwidth below -10 dB is 112 MHz. In addition, since the gain of the antenna is -4 dBi, it has the omnidirectional radiation characteristic, so it can be applied to various fields as an antenna for mobile devices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.185-195
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• 2021

The flapping-wing micro air vehicle (FW-MAV) in this study utilizes the cambered wings made of quite flexible material. Similar to the flying creatures, the present cambered wing uses three different materials at its leading edge, vein, and membrane. And it is constrained in various conditions. Since passive rotation uses the flexible nature of the wing, it is important to select an appropriate material for a wing. A three-dimensional fluid-structure interaction solver is developed for a realistic modeling of the cambered wing. Then a parametric study is conducted to evaluate the aerodynamic performance in terms of the elastic modulus of leading edge and vein. Consequently, the elastic modulus plays a key role in enhancing the aerodynamic performance of FW-MAVs.

• Journal of Aerospace System Engineering
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• v.18 no.2
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• pp.21-28
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• 2024

In light of the rapid development of the space industry, there has been increased attention on small satellites. These satellites rely on components that are considered to have lower reliability compared to larger-scale satellites. As a result, predicting reliability becomes even more crucial in this context. Therefore, this study aims to compare three reliability prediction techniques: MIL-HDBK-217F, RiAC-HDBK-217Plus, and FIDES. The goal is to determine a suitable reliability standard specifically for nano-satellites. Furthermore, we have refined the quality assurance factors of the manufacturing company. These factors have been adjusted to be applicable across various industrial sectors, with a particular focus on the selected FIDES prediction standard. This approach ensures that the scoring system accurately reflects the suitability for the aerospace industry. Finally, by implementing this refined system, we confirm the impact of the manufacturer's quality assurance level on the total failure rate.