• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.276-285
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• 2020

In this study, accelerated chloride diffusion tests were performed on OPC(Ordinary Portland Cement) and FA(Fly Ash) concrete considering three levels o f W/B(Water to Binder) ratio o n 1,095 curing days. The accelerated chloride diffusion coefficient and the passed charge were evaluated in accordance with Tang's method and ASTM C 1202, and the resistance performance to chloride attack improved over time. FA concrete showed excellent resistance performance against chloride penetration with help of pozzolanic reaction. As the result of the passed charge, FA concrete showed durability improvement, "low" grade to "very low" grade, but OPC concrete changed "moderate" grade to "low" grade at 1,095 curing days. After assuming the design variables used for durability design as normal distribution functions, the service life of each case was evaluated by the probabilistic analysis method based on MCS(Monte Carlo Simulation). In FA concrete, the increase of probability of durability failure was lower than that of OPC concrete with increasing time, because the time-dependent coefficient of FA concrete was up to 3.2 times higher than OPC concrete. In addition, the service life by probabilistic analysis was evaluated lower than the service life by deterministic analysis, since the target probability of durability failure was set to 10%. It is considered that more economical durability design will be possible if the mo re suitable target probability of durability failure is set for various structures through researches on actual conditions and indoor tests under various circumstances.

• The korean journal of orthodontics
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• v.27 no.3 s.62
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• pp.359-372
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• 1997

This study was conducted to discern differences of craniofacial, dentoalveolar structure and model measurements between sex and between class n openbite group and non-openbite group. The sample consisted of 49 adult patients with class Il malocclusion. 24 linear measurements, 22 angular measurements and 12 ratios were selected in lateral cephalometry. Also, arch width, length, anterior crowding, average molar relation were measured or calculated in diagnostic model. The data were evaluated by t-test and multiple discriminant analysis. The results were as follows, 1. Most linear measurements, with the exception of MnBL and AUDH, were significantly larger in male(p<0.05). but, intermaxillary relations and spatial position of maxilla and mandible relative to cranial base were not different for both sex. 2. With the exception of upper and lower anterior crowding, lower arch width, upper arch length, AMR, male exhibited significantly larger measurements in model analysis (p<0.05). 3. Size differences of maxilla and mandible between openbite and non-openbite group were not significant(p>0.05). but openbite group showed significantly increased genial angle(p<0.05), FH-CoGo(p<0.01), FH-NA(p<0.01) and FH-NB, FH-NPog (p<0.05). 4. ALFH and PUDH were larger(p<0.05) in openbite group. this result served as compensation for the spatial position of mandible relative to cranial base. AUPUDH (p<0.001) and ALPLDH(p<0.05) were lower in openbite group. upper anterior crowding was the only measurement which showed difference between openbite and non-openbite group(p<0.05). 5. For the purpose of classifying adult class n openbite and non-openbite group, multiple discriminant analysis was done genial angle, ALPLDH, AUPUDH, FH-NA were included in multiple discriminant equation. 39 cases($92.86\%$) were correctly classified when applied to the sample used in this study.

• Applied Chemistry for Engineering
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• v.24 no.3
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• pp.219-226
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• 2013

Organic semiconductor-based soft electronics has potential advantages for next-generation electronics and displays, which request mobile convenience, flexibility, light-weight, large area, etc. Organic field-effect transistors (OFET) are core elements for soft electronic applications, such as e-paper, e-book, smart card, RFID tag, photovoltaics, portable computer, sensor, memory, etc. An optimal multi-layered structure of organic semiconductor, insulator, and electrodes is required to achieve high-performance OFET. Since most organic semiconductors are self-assembled structures with weak van der Waals forces during film formation, their crystalline structures and orientation are significantly affected by environmental conditions, specifically, substrate properties of surface energy and roughness, changing the corresponding OFET. Organo-compatible insulators and surface treatments can induce the crystal structure and orientation of solution- or vacuum-processable organic semiconductors preferential to the charge-carrier transport in OFET.

• Journal of the Mineralogical Society of Korea
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• v.28 no.2
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• pp.127-133
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• 2015

Li-bearing muscovite is commonly found along with trioctahedral lepidolite in granitic pegmatites. Structurally, $Li^+$ ions can replace $K^+$ ions in the interlayer (Int) of muscovite or incorporate into vacancies of the dioctahedral sheet (Sub). However, detailed mechanism of the lithium incorporation into muscovite is challenging to investigate using experimental techniques alone. In the current study, density functional theory (DFT) has been applied to examine the crystal structure and energy variation when $Li^+$ resides in the interlayer or the octahedral sheet. Depending on the position of $Li^+$ (i.e., Int vs. Sub), DFT showed significant differences in the mica's structures such as lattice parameters, sheet thickness, interlayer separation, and OH angles with respect to the ab plane. DFT further showed that, in pure muscovite, $Li^+$ has a lower energy when it is located in Int than Sub. By contrast, in the case of $Fe^{2+}$ substitution into the octahedral sheet, $Li^+$ has a lower energy in Sub than in Int. These results imply that $Li^+$ incorporates into the Al octahedral sheets only when the octahedral sheets possess structural charges, suggesting cation substitution in the octahedral sheets plays an important role in the Li incorporation mechanism into muscovite. They can also explain the experimental observation about the positive relationship between $Fe^{2+}$ and $Li^+$ amounts in Li-bearing muscovite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.190-190
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• 2008

자연적으로 발생되는 파도, 비, 우박 등과 철도, 차량 및 엘리베이터 등과 같은 인위적인 설치, 이동에 의해 발생되는 진동에너지는 우리 일상생활에서 가장 흔하게 발생할 수 있는 에너지원인데, 이러한 진동에너지는 압전 소재를 이용하여 재생 가능하여 최근에는 이에 대한 연구가 활발히 진행되어 왔다. 예를 들면, 미국의 MIT에서는 인간이 걸을 때 신발에 가해지는 압력을 이용하여 전력을 발생시키는 연구를 진행하여 2.9 mW의 전력을 얻었다. 특히 이러한 기술은 인간의 걷기 운동 등과 같은 일상적인 동작으로 필요한 전력을 얻을 수 있고, 세라믹 소자를 이용하기 때문에 전자노이즈가 발생되지 않을 뿐 아니라 반영구적으로 사용할 수가 있어서, 소형 전자기기 등에 서 기존 이차전지를 대체 또는 보완 할 수 있는 기술로 검토되고 있다. PZT계 세라믹스는 높은 유전상수와 우수한 압전특성으로 이러한 압전발전 분야에서 가장 널리 사용되어지고 있다. 하지만 에너지 효율을 높이기 위하여 적층 구조의 제작 시 구조적 특성상 내부전극이 도포된 상태에서 동시 소결이 필요한데, $1000^{\circ}C$ 이상의 높은 소결온도 때문에 소재 원가가 낮은 Ag전극 대신 값비싼 Pd나 pt가 다량 함유된 Ag/Pd, Ag/Pt 전극이 사용되고 있어 경제성이 떨어지는 단점을 갖게 된다. 순수 Ag 전극을 사용하거나 Ag의 비율이 높은 내부전극을 사용하기 위해서는 $900^{\circ}C$ 이하에서 소결되고 우수한 전기적 특성을 보이는 압전 세라믹스 소재를 개발 하는 것이 필요하다. 따라서 본 연구에서는 압전특성이 우수한 $(Pb_{1-x}Cd_x)(Ni_{1/3}Nb_{2/3})_{0.25}(Zr_{0.35}/Ti_{0.4})O_3$ 계의 조성을 설계하고, 소결온도를 낮추기 위해서 2 단계 하소법을 이용하였다. 또한 $MnCO_3$, $SiO_2$, $Pb_3O_4$ 등을 소랑 첨가하여 액상 소걸 특성을 부여하여 소결 온도를 감소시키려는 시도도 하였다. 소결체의 전체적인 제조 공정은 일반적인 벌크 세라믹의 소걸 공정을 따랐다. 최종 소결된 시편을 XRD분석을 통하여 상을 확인하였고 SEM을 이용하여 미세조직을 관찰 하였다. 전기적 특성을 평가하기 위하여 두께를 1mm로 연마한 시편에 Ag 전극을 도포하여 $650^{\circ}C$ 에서 열처리한 후, 분극처리 하였다. Impedance analyzer를 이용하여 압전 특성 (전기기계결합계수 및 기계적품질계수)을 측정 하였고, 압전전하상수는 $d_{33}$-meter로 측정하였다. 본 연구에서는 압전체에 가해지는 하중의 크기, 시편의 크기, 하중을 가하는 방법, 에너지 저장회로의 최적화 등을 다양하게 시도하면서 에너지 변환 및 저장 효율을 평가하였다.

• Journal of IKEEE
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• v.15 no.1
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• pp.23-28
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• 2011

This paper describes design and implementation of a spread spectrum clock generator(SSCG). The proposed architecture generates the spread spectrum clock controlling a input voltage signal for VCDL(Voltage Controlled Delay Line). Spread charge pump is controlled by the SSC modulation logic block provides a control signal to VCDL through LPF in DLL. By using this architecture, chip area and power consumption can be reduced because it is not necessary additional circuit to control modulation rate. This circuit has been designed and fabricated using the UMC 0.25um CMOS technology. The chip occupies an area of 290${\times}$120um^2.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.152-152
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• 2015

최근에 백색 발광체 개발에 많은 관심이 고조되고 있다. 본 연구에서는 고상반응법을 사용하여 활성제 이온 $Dy^{3+}$의 함량을 0.05 mol로 고정하고, $Eu^{3+}$ 이온의 함량을 각각 0, 0.5, 1, 5, 10, 15 mol%로 변화시켜 $Y_2WO_6:Dy^{3+}$, $Eu^{3+}$ 형광체 분말을 합성하였다. $Dy^{3+}$ 이온만 도핑된 $Y_2WO_6$ 형광체의 흡광 수펙트럼은 전하 전달 밴드 ($Dy^{3+}-O^{2-}$)에 의한 250~350 nm에 존재 하는 밴드폭이 넓은 전이 신호와 360~500 nm 영역에 걸쳐 있는 상대적으로 흡광 세기가 약한 다수의 $Dy^{3+}$ 이온의 전이 신호가 관측 되었다. $Dy^{3+}$와 $Eu^{3+}$가 동시 도핑된 $Y_2WO_6$ 형광체의 발광 스펙트럼의 경우에, $Eu^{3+}$ 이온의 몰 비가 증가함에 따라 $Dy^{3+}$ 이온에 의한 577 nm에 주 피크를 갖는 황색 발광 파장의 세기는 감소하였고, $Eu^{3+}$ 이온에 의해 발생하는 612 nm의 적색 발광 파장의 세기는 순차적으로 증가하였다. 이 결과는 $Dy^{3+}$와 $Eu^{3+}$ 이온의 몰 비를 적절히 조절함으로써 최적의 백색 발광 형광체를 제조할 수 있음을 제시한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.5
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• pp.42-47
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• 2004

This research has improved the problem of discharge AND gate PDP proposed before. The polarity of the DC discharge which composes AND gate is reversely designed and the cross talk problem to the adjacent scanning electrode has been improved. The AND gate proposed before operated by using non-linearity of the discharge by the space charge. In this research, new discharge NOT logic in which it was used that an applied voltage changed with the discharge circuit was added to AND gate. AND gate came to operate more stably. A selective address was able to be discharged with four horizontal scanning electrodes from the experiment result. The operation margin of the AND gate discharge obtained 34V and of the address discharge obtained 70V.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.2
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• pp.87-94
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• 2001

A soft error rate for DRAM was predicted in connection with the leakage current in cell capacitor. The charge in cell capacitor was decreased during the DRAM operation, and soft error retes due to the leakage current were calculated in various operation mode of DRAM. It was found that the soft error rate of the /bit mode was dominant with small leakage current, but as increasing the leakage current memory mode shown the dominant effect on soft error rate. Using the 256M grade DRAM structure it was predicted that the soft error rate was influenced by the change of the cell capacitance, bit line capacitance, and the input voltage sensitivity of sense amplifier, and these results can be used to the design of the optimum cells in the next generation DRAM development.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.319-324
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• 2012

This paper introduces a 2-dimensional touch screen panel driver based on an improved capacitive sensing circuit. The improved capacitive sensing circuit based on charge pump can eliminate the remaining charges of the intermediate nodes, which may cause output voltage drift. The touch screen panel driver with mixed-mode circuits was built and simulated using Cadence Spectre. Verilog-A models the digital circuits effectively and enables them to interface with analog circuits easily. From the simulation results, we can verify the reliable operations of the simple structured touch screen panel driver based on the improved capacitive sensing circuit offering no voltage drift.