• Journal of KSNVE
• /
• v.7 no.6
• /
• pp.899-908
• /
• 1997

본 글에서는 소형 압축기 셸과 같은 비교적 복잡한 기계 구조물의 간접적 입력 측정에 대한 결과 및 직접 측정과의 비교를 기술하였고 다수 응답의 동시 측정에 따른 문제점을 해결코자 기준점을 이용한 전달함수의 측정 방법을 제시 하였다. 하부 빈 셸에 대한 실험 결과, 압축기의 셸과 같은 비교적 복잡한 구조물에 대해서도 간접 입력 측정을 상당한 신뢰성을 갖고 시도할 수 있으며 특히 공진점이나 영점 부근에서의 추정 오차는 측정점의 갯수를 증대시킴으로써 크게 개선 시킬수 있음을 보여주었다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.6
• /
• pp.933-941
• /
• 1997

In the analysis of thin elastic structures such as plate and shell-like structures, classical lower-order theories like Kirchhoff and Reissner-Mindin theories are insufficient to describe the behavior of such structures in the region where the state of stresses is complex. On the other hand, the fully three dimensional theory of linear elasticity can provide desired analysis accuracy, but requires expensive computational implementation compared to the classical theories. This paper is concerned with the development of hierarchical models for elastic structures which can be used for hierarchical modeling for the analysis of such structures. Derivation and limit model analysis (when the thickness of structures tends to zero) of hierarchical models are presented together with a introduction of modeling error estimation. Also, numerical results supporting theoretical results are given.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.10
• /
• pp.825-829
• /
• 2015

Theoretical calculations suggest that the thermoelectric figure of merit (ZT) can be improved by introducing a core-shell heterostructure to a semiconductor nanowire because of the reduced thermal conductivity of the nanowire. To experimentally verify the decrease in thermal conductivity in core-shell nanowires, the thermal conductivity of Ge-SixGe1-x core-shell nanowires grown by chemical vapor deposition (CVD) was measured using suspended microdevices. The silicon composition (Xsi) in the shells was measured to be about 0.65, and the remainder of the germanium in the shells was shown to play a role in decreasing defects originating from the lattice mismatch between the cores and shells. In addition to the standard four-point current- voltage (I-V) measurement, the measurement configuration based on the Wheatstone bridge was attempted to enhance the measurement sensitivity. The measured thermal conductivity values are in the range of 9-13 W/mK at room temperature and are lower by approximately 30 than that of a germanium nanowire with a comparable diameter.

• Journal of KSNVE
• /
• v.2 no.2
• /
• pp.92-95
• /
• 1992

자동차에 사용되는 경음기는 자동차들 사이뿐만 아니라 특히 보행자에게 경적음을 발생하여 사고를 사전에 방지하기 위하여 사용되는 자동차의 필수 부품 이다. 일반적으로 경음기는 2가지 특성에 의해 특정지워 질 수 있는데 이는 음압과 주파수(음색) 특성이다. 이들 모두는 규격에 의하여 제한되는 요소들로서, 전자의 경우 너무 소리가 적게되면 경음기로서의 기능을 상실하게 되며 지나치게 크게 되면 상대방 및 주위에 지나치게 크게 피해를 주게 되는 요소이다. 후자의 경우 동일한 크기의 음압이라도 그것을 구성하는 특성에 따라 인간에게 주어지는 소음에 의한 심리적 영향이 달라지게 되므로 불쾌음의 발생을 지양해야 한다. 이 글에서는 같은 음의 세기라도 상대적으로 부드러운 음색을 갖는 셸(shell)형 경음기의 특성 및 개발 결과에 대하여 언급하고자 한다.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2023.07a
• /
• pp.197-198
• /
• 2023

드론 기술이 발전함에 따라, 최근에는 재난 구조 및 교통 관측, 과학 연구와 같은 분야에서 드론이 활용됨으로써, 사회적 및 산업적 발전에 일조하는 실정이다. 그러나 드론의 사용률이 증가하는 상황에서, 다양한 취약점을 내포한 드론으로 인하여, 심각한 보안위협이 발생하는 문제점이 존재한다. 이에 따라, 드론에서 발생하는 보안위협에 대응하기 위한 연구가 요구되며, 본 논문은 대응방안을 도출하기 위한 목적으로, 드론에서 발생 가능한 신규 취약점을 분석하고 실증한다. 본 논문에서 발굴한 신규 취약점은 A 드론을 대상으로, 기존의 다중 접속 취약점을 악용한 FTP 및 TELNET 접속 취약점이며, FTP 접속으로 암호화된 파일에 접근이 가능하고 TELNET 접속으로 루트 권한의 셸을 실행하는 신규 취약점을 발굴하였다.

• Membrane Journal
• /
• v.30 no.4
• /
• pp.228-241
• /
• 2020

Separators, which produces physical layer between a cathode and anode, are getting enormous attention as the quality of the separator determines the performance of lithium ion batteries (LIBs). Porous membranes based on polyethylene (PE) and polypropylene (PP) are generally utilized as the separator of LIBs because of their high electrochemical stability and suitable mechanical strength. However, low thermal resistance and wettability of PE and PP membranes limited the potential of LIBs. Operating at the temperature exceeding the melting point of membranes, the separators change their structures which lead to short circuit of LIBs. Low wettability of the separators corresponds to low ionic conductivity which increases the cell resistance. To overcome these weaknesses of PE and PP separators, different types of separator were prepared by co-electrospinning, applying coating layer, forming core shell around membrane, and papermaking method. The synthesized separator greatly enhanced the heat resistance and wettability of separator and mechanical properties like flexibility and tensile strength. In this review different type of polymer membrane used as separator in lithium ion battery are discussed.

• Journal of the Korean Wood Science and Technology
• /
• v.46 no.1
• /
• pp.17-28
• /
• 2018

In this study, catalytic activation using sulfuric acid lignin (SAL), the condensed solid by-product from saccharification process, with potassium hydroxide at $750^{\circ}C$ for 1 h in order to investigate its potential to nanoporous carbon In this study, catalytic activation using sulfuric acid lignin (SAL), the condensed solid by-product from saccharification process, with potassium hydroxide at $750^{\circ}C$ for 1 h in order to investigate its potential to nanoporous carbon material. Comparison study was also conducted by production of activated carbon from coconut shell (CCNS), Pinus, and Avicel, and each activated carbon was characterized by chemical composition, Raman spectroscopy, SEM analysis, and BET analysis. The amount of solid residue after thermogravimetric analysis of biomass samples at the final temperature of $750^{\circ}C$ was SAL > CCNS > Pinus > Avicel, which was the same as the order of activated carbon yields after catalytic activation. Specifically, SAL-derived activated carbon showed the highest value of carbon content (91.0%) and $I_d/I_g$ peak ratio (4.2), indicating that amorphous large aromatic structure layer was formed with high carbon fixation. In addition, the largest changes was observed in SAL with the maximum BET specific surface area and pore volume of $2341m^2/g$ and $1.270cm^3/g$, respectively. Furthermore, the adsorption test for three kinds of organic pollutants (phenol, 2,4-Dichlorophenoxyacetic acid, and carbofuran) were conducted, and an excellent adsorption capacity more than 90 mg/g for all activated carbon was determined using 100 ppm of the standard solution. Therefore, SAL, a condensed structure, can be used not only as a nanoporous carbon material with high specific surface area but also as a biosorbent applied to a carbon filter for remediation of organic pollutants in future.