• Applied Chemistry for Engineering
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• v.20 no.3
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• pp.322-328
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• 2009

Emulsion polymerization of octamethylcyclotetrasiloxane (OMCTS) was conducted under ultrasonic irradiation. Two sources of ultrasound with different intensities and frequencies of 20 KHz and 40 KHz were used for horn and bath type reactor, respectively. A combined process of horn and bath was also investigated. The effectiveness of the reaction systems was investigated by measuring conversion as well as intrinsic viscosity of the products. The influence of reaction temperature and sonication time on the progress of sonochemical polymerization was examined. It was found that conversion of greater than 80% and high viscosity were achieved within a few minutes of sonication in a horn type reactor, however, conversion and viscosity showed maximum values depending upon the sonication time. In a bath type reactor where a relatively weak intensity was maintained, longer duration time of more than one hour of sonication was required to reach a high level of conversion and viscosity. Compared with the horn type system, the conversion and viscosity in the bath type reactor were increased along with the sonication time. When the polymerization was carried out in a combined system of horn and bath, the evolution of conversion and molecular weight was quite different from the other cases. For the given geometry of reaction system, acoustic analysis using a commercial software was carried out and the results were correlated with experimental observation.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.2
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• pp.150-159
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• 2013

To enhance the performance of SEWGS system by holding the WGS catalyst in a SEWGS reactor using bed inserts, effects of insert geometry and shape of WGS catalysts on CO conversion were measured and investigated. Small scale fluidized bed reactor was used as experimental apparatus and WGS catalyst (particle and tablet) and sand were used as bed materials. The parallel wall type and cross type bed inserts were used to hold the WGS catalysts. The CO conversion with steam/CO ratio was determined based on the exit gas analysis. The measured CO conversion using the bed inserts showed high value comparable to physical mixing cases. Moreover, gas flow direction was confirmed by bed pressure drop measurement for each case. Most of input gas flowed through the catalyst side when we charged tablet type catalyst into the bed insert and this can cause low $CO_2$ capture efficiency because the possibility of contact between input gas and $CO_2$ absorbent is low in this case. New bed insert geometry was proposed based on the results from this study to enhance contact between input gas and WGS catalyst and $CO_2$ absorbent.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.189-192
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• 1998

In this paper, we analyzed Microwave-DC conversion efficiency for the rectennas and it's position change. Rectenna consist of a two major parts, receiveing antenna and rectifying circuits. We made two types of 2.45C rectennas which the dipole and the patch antenna. Rectifying circuit is a GaAs-schottky diode with a large forward current and reverse breakdown voltage. The results of RF-DC conversion efficiency for two rectennas, patch type has 75.6% efficiency with 400$\Omega$ load resistor and dipole type has 69.75% efficiency with 360$\Omega$ load resistor. When the rectennas has optimal load resistor, Rectenna efficiency shows of $\pm10%$ at $70^{\circ}$~$110^{\circ}$ position.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.249-256
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• 2009

The cooling technology of power conversion semiconductors in the propulsion system for the HEMU(High Electrical Multi Unit) are applied in water cooling method and phase change method such as the immersed type and the heat pipe type. This research designs and manufactures the water cooling system that could cool about heat load Q=2kW and performance tests to apply it by an electric power conversion semiconductors(IGBT) cooling technology. Experimental condition made change of a flow rate, an air velocity and a heat load to confirm operation characteristics of water cooling device, and when is heat load 2kW, air velocity 20 m/s, and water flow rate 7kg/s, it is about $80^{\circ}C$ to temperature of cooling plate.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.1
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• pp.159-168
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• 2010

In the recent years, power analysis attacks were widely investigated, and so various countermeasures have been proposed. In the case of block ciphers, masking methods that blind the intermediate results in the algorithm computations(encryption, decryption, and key-schedule) are well-known. The type conversion of masking is unavoidable since Boolean operation and Arithmetic operation are performed together in block cipher. Messerges proposed a masking type conversion algorithm resistant general power analysis attack and then it's vulnerability was reported. We present that some of exiting attacks have some practical problems and propose a new power analysis attack on Messerges's algorithm. After we propose the strengthen DPA and CPA attack on the masking type conversion algorithm, we show that our proposed attack is a practical threat as the simulation results.

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.89-96
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• 2010

This paper describes the methodology of calculating the internal dose conversion coefficient in order to assess the radiological impact on non-human species. This paper also presents the internal dose conversion coefficients of 25 radionuclides ($^3H,\;^7Be,\;^{14}C,\;^{40}K,\;^{51}Cr,\;^{54}Mn,\;^{59}Fe,\;^{58}Co,\;^{60}Co,\;^{65}Zn,\;^{90}Sr,\;^{95}Nb,\;^{99}Tc,\;^{106}Ru,\;^{129}I,\;^{131}I,\;^{136}Cs,\;^{137}Cs,\;^{140}Ba,\;^{140}La,\;^{144}Ce,\;^{238}U,\;^{239}Pu,\;^{240}Pu$) for domestic seven reference animals (roe deer, rat, frog, snake, Chinese minnow, bee, and earthworm) and one reference plant (pine tree). The uniform isotropic model was applied in order to calculate the internal dose conversion coefficients. The calculated internal dose conversion coefficient (${\mu}Gyd^{-1}$ per $Bqkg^{-1}$) ranged from $10^{-6}$ to $10^{-2}$ according to the type of radionuclides and organisms studied. It turns out that the internal does conversion coefficient was higher for alpha radionuclides, such as $^{238}U,\;^{239}Pu$, and $^{240}Pu$, and for large organisms, such as roe deer and pine tree. The internal dose conversion coefficients of $^{239}U,\;^{240}Pu,\;^{238}U,\;^{14}C,\;^3H$, and $^{99}Tc$ were independent of the organism.

• Journal of Power Electronics
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• v.12 no.2
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• pp.317-325
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• 2012

Resonant immittance converter (RIC) topologies can transform a current source into a voltage source (Type-I RICs) and vice versa (Type-II RICs), thereby making them suitable for many power electronics applications. RICs are operated at a fixed frequency where the resonant immittance network (RIN) exhibits immittance conversion characteristics. It is observed that the low-frequency response of Type-II RINs is relatively flat and that the state variables associated with Type-II RINs affect the response only at the high frequencies in the vicinity of the switching frequency. The overall response of a Type-II RIC is thus dominated by the filter response, which is particularly important for the controller design. Therefore, an approximate equivalent circuit model and a small-signal model of Type-II RICs are proposed in this paper, neglecting the high-frequency response of Type-II RINs. While the proposed models greatly simplify and speed-up the analysis, it adequately predicts the open-loop transient and small-signal ac behavior of Type-II RICs. The validity of the proposed models is confirmed by comparisons of their results with those obtained from a cycle-by-cycle simulation and with an experimental prototype.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.19 no.6
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• pp.101-110
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• 2016

Development activities in forest areas are analysed based on degree of slope, altitude, land cover, and prefectures in order to improve the capacity of existing regulations of 'feasibility of forest land conversion' and 'assessment of forest land characteristics' in this research. 959 land based developments between year 2007 and 2013 have been analysed. A development site includes over 50% of forest is categorized as a forest type, degree of slope is steeper than $8.5^{\circ}$ as mountain type, and a development included in the both categories as combined type. Distribution characteristics of the above three types are analysed by development categories and regions adopting Relative Mountain Development Index(RMDI). In results, 44.94% of total development activities have been carried out in Gyeongsang Do in order of urban development, industrial complex, sports facilities, and soil and stone collection quarrying. Developments less than $0.3km^2$ which are exempt from the feasibility of forest land conversion regulation consist 86 cases of forest type, 78 cases in mountain type, and 78 cases in combined type. SAI by slope range showed the highest value of 1.55 in less than $5^{\circ}$ and the lowest value of 0.69 between $20^{\circ}-25^{\circ}$. RMDI value in Gyeongsang Do where mountain ratio is 67.05% appeared 1.17, which is 5 times more than Gangwon Do where mountain area ratio is 81.30%, and 2 times more than Chungchung Do where mountain area ratio is 51.24%. Development activities in forestland in Korea showed unequal distributions and 26% of those developments were not subjected to the feasibility of forest land conversion regulation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.67-67
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• 2011

Compound semiconductor/CNTs composites have shown considerably improved efficiency improvement in photovoltaic devices, which is often attributed to two different factors. One is the formation of efficient electronic energy cascade structures. The other effect of CNTs on the performance of photovoltaic devices is the decrement of interfacial resistance. The interfacial resistances at n-type/ p-type materials and/or n-type materials/TCO electrode are reduced by an outstanding electrical property of CNTs. In addition to the effects of CNTs, we report the third reason for increment of efficiency in photovoltaic devices by CNT's well-known electrical field enhancement effects. The improved ${\beta}$ values in reverse-FE currents of CIGS electrode with SWNTs layers indicate the enhancement of electrical field in photovoltaic devices, which implies the acceleration of the electron transfer rate in the cell. Due to the formation of an efficient electronic energy cascade structure and the decrease of the interfacial resistance as well as the improvement of the electrical field in the photovoltaic devices, the power conversion efficiency of electrochemically deposited superstrate-type CIGS solar cells was increased 24.3% in the presence of SWNTs and showed 10.40% conversion efficiency.

• Korean Journal of Optics and Photonics
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• v.9 no.5
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• pp.282-290
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• 1998

The equivalent lens conversion technique is applied to design achromatic doublet and aplanatic doublet. A thin doublet which has zero axial thicknesses, are corrected for the third order aberrations at first, and the thin doublet is converted into thick lens system by using the equivalent lens conversion. Two types of cemented doublets, the Fraunhofer type and the Steinheil type, are designed by using a crown glass BaK-2 and a flint glass SF-2. In the thin doublet design, there are two achromatic solutions and a aplanatic solution for the both types.