• Advances in nano research
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• 제9권4호
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• pp.237-250
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• 2020

An accurate plate theory for assessing sandwich structures is of interest in order to provide precise results. Hence, this paper develops Layer-Wise (LW) theory for reaching precise results in terms of buckling and vibration behavior of Functionally Graded Carbon Nanotube-Reinforced Composite (FG-CNTRC) annular nanoplates. Furthermore, for simulating the structure much more realistic, its edges are elastically restrained against in-plane and transverse displacement. The nano structure is integrated with piezoelectric layers. Four distributions of Single-Walled Carbon Nanotubes (SWCNTs) along the thickness direction of the core layer are investigated. The Differential Quadrature Method (DQM) is utilized to solve the motion equations of nano structure subjected to the electric field. The influence of various parameters is depicted on both critical buckling load and frequency of the structure. The accuracy of solution procedure is demonstrated by comparing results with classical edge conditions. The results ascertain that the effects of different distributions of CNTs and their volume fraction are significant on the behavior of the system. Furthermore, the amount of in-plane and transverse spring coefficients plays an important role in the buckling and vibration behavior of the nano-structure and optimization of nano-structure design.

• 설비공학논문집
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• 제28권4호
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• pp.158-164
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• 2016

Currently, identifying a new carbon-free energy resource is important in order to resolve the global warming problem. Along the same line, this paper studied how to convert magnetic force into mechanical force and a new basic mechanism of converting magnetic force into mechanical force was identified. Long-term reliability test, around 15 million times, was also conducted at $-1^{\circ}C{\sim}27^{\circ}C$ to evaluate the durability of magnetic force. As a result, tests showed that the deviation of the mechanical force was within 0.8% of the initial force, and the relation between repulsive force (P) and ambient temperature (T) was formulated in a linear equation P = -0.175T+78.945.

• Journal of Electrochemical Science and Technology
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• 제7권2호
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• pp.91-96
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• 2016

Oxidation behaviours of ash free coal (AFC), carbon, and H₂ fuels were investigated with a coin type molten carbonate fuel cell. Because AFC has no electrical conductivity, its oxidation occurs via gasification to H₂ and CO. An interesting behaviour of mass transfer resistance reduction at higher current density was observed. Since the anode reaction has the positive reaction order of H₂, CO₂ and H₂O, the lack of CO₂ and H₂O from AFC results in a significant mass transfer resistance. However, the anode products of CO₂ and H₂O at higher current densities raise their partial pressure and mitigate the resistance. The addition of CO₂ to AFC reduced the resistance sufficiently, thus the resistance reduction at higher current densities did not appear. Electrochemical impedance results also indicate that the addition of CO₂ reduces mass transfer resistance. Carbon and H₂ fuels without CO₂ and H₂O also show similar behaviour to AFC: mass transfer resistance is diminished by raising current density and adding CO₂.

• Biomolecules & Therapeutics
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• 제6권3호
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• pp.247-255
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• 1998

Carbon tetrachloride (CCI$_4$) induces the hepatotoxicity due to the reactive free radicals generated by cytochrome P-450 (CYP-450) enzyme, which result in destabilization of cellular membrane. Diltiazem, a calcium channel blocking agent, has been known to suppress the CYP-450 enzyme activities. To study the effect of diltiazem in $CCl_4$-treated rats, we measured the activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and glutathione S-transferase (GST), contents of bilirubin, albumin, total protein, cholesterol, triglyceride, blood urea nitrogen, creatinine malondialdehyde and calcium. Also we conducted liver histopathologic examinations. Diltiazem, when administered 1 hour prior to CCI$_4$ treaeent, significantly reduced the activities of ALT and AST, the contents of microsomal malondialdehyde and calcium in liver and microsome as compared with those of $CCl_4$-treated rats. In addition, histopathologic examination showed that diltiazem prevented the development of centrilobular necrosis induced by CCI$_4$ in liver tissue. Our results suggested that diltiazem could inhibit the formation of free radicals and the influx of calcium. Therefore diltiazem may be applied to suppress the liver damage caused by $CCl_4$.

• Advances in nano research
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• 제8권4호
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• pp.307-322
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• 2020

In this article, free vibration of double-walled carbon nanotubes (DWNT) based on nonlocal Kelvin's model have been investigated. For this purpose, a nonlocal Kelvin's model is established to observe the small scale effect. The wave propagation is employed to frame the governing equations as eigenvalue system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. The new set of inner and outer tubes radii investigated in detail against aspect ratio. The influence of boundary conditions via nonlocal parameter is shown graphically. Due to small scale effect fundamental frequency ratio decreases as length to diameter ratio increases. Small scale effect becomes negligible on all end supports for the higher values of aspect ratio. With the smaller inner tube radius double-walled CNT behaves more sensitive towards nonlocal parameter. The results generated furnish the evidence regarding applicability of nonlocal model and also verified by earlier published literature.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.431-454
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• 2016

In this paper, the nonlinear static and free vibration analysis of Euler-Bernoulli composite beam model reinforced by functionally graded single-walled carbon nanotubes (FG-SWCNTs) with initial geometrical imperfection under uniformly distributed load using finite element method (FEM) is investigated. The governing equations of equilibrium are derived by the Hamilton's principle and von Karman type nonlinear strain-displacement relationships are employed. Also the influences of various loadings, amplitude of the waviness, UD, USFG, and SFG distributions of carbon nanotube (CNT) and different boundary conditions on the dimensionless transverse displacements and nonlinear frequency ratio are presented. It is seen that with increasing load, the displacement of USFG beam under force loads is more than for the other states. Moreover it can be seen that the nonlinear to linear natural frequency ratio decreases with increasing aspect ratio (h/L) for UD, USFG and SFG beam. Also, it is shown that at the specified value of (h/L), the natural frequency ratio increases with the increasing the values amplitude of waviness while the dimensionless nonlinear to linear maximum deflection decreases. Moreover, with considering the amplitude of waviness, the stiffness of Euler-Bernoulli beam model reinforced by FG-CNT increases. It is concluded that the R parameter increases with increasing of volume fraction while the rate of this parameter decreases. Thus one can be obtained the optimum value of FG-CNT volume fraction to prevent from resonance phenomenon.

• 한국결정학회지
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• 제13권2호
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• pp.69-72
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• 2002

본 연구에서는 적층판 자유단 근처에서의 층간응력 문제를 해석하였다. 탄소섬유 복합적층판 [+40/-40］s과 탄소 부직포가 삽입된 적층판 ［+40//-40］s 이 인장하중을 받고 있는 경우에 대하여 해석한다. 부호 “//”는 층간에 부직포가 위치함을 의미한다. 부직포를 삽입함으로서 모우드 Ⅱ의 층간파괴인성치는 크게 증가하지만 모우드 I의 값은 크게 변하지 않음이 보고되어 있다./sup 3)/ 복합재료 구조물에 있어서 모우드 Ⅲ 층간파괴인성치가 중요하지만 그 값을 실험적으로 평가하기는 어렵다. 따라서, 본 연구에서는 부직포 효과 특히, 적층판 자유단 근처에서의 모우드 Ⅲ층간파괴 특성을 이해하기 위하여 유한요소 해석을 통해 전단응력을 분석하고자 한다.

• 한국세라믹학회지
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• 제49권6호
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• pp.523-527
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• 2012

Silicon carbide (SiC) has recently drawn an enormous amount of industrial interest due to its useful mechanical properties, such as its thermal resistance, abrasion resistance and thermal conductivity at high temperatures. In this study, RF thermal plasma (PL-35 Induction Plasma, Tekna CO., Canada) was utilized for the synthesis of high-purity SiC powder from an organic precursor (hexamethyldisilazane, vinyltrimethoxysilane). It was found that the SiC powders obtained by the RF thermal plasma treatment included free carbon and amorphous silica ($SiO_2$). The SiC powders were further purified by a thermal treatment and a HF treatment, resulting in high-purity SiC nano-powder. The particle diameter of the synthesized SiC powder was less than 30 nm. Detailed properties of the microstructure, phase composition, and free carbon content were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), a thermogravimetric (TG) analysis, according to the and Brunauer-Emmett-Teller (BET) specific surface area from N2 isotherms at 77 K.

• 열처리공학회지
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• 제19권2호
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• pp.90-95
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• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.

• 한국표면공학회지
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• 제55권1호
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• pp.18-23
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• 2022

Presence of cracks in electrodeposited hard chromium layer, which provide a path of corrosive media to steel substrate, is a serious issue in metal finishing with chromium electroplating. In this study, we added sodium molybdate in an electrolyte for chromium electroplating bath. 130g/L of sodium molybdate in Sargent bath for chromium electroplating causes a codepostion of molybdenum with chromium in a rage of 0.61 ~ 3.14 wt.%. The co-deposited molybdenum enhances the crystallinity of chromium layer, thus the hardness is slightly decreases by the addition of molybdate in electrolyte. However, due to the co-deposition of molybdenum, a crack-free chromium layer could be electrodeposited. Such crack-free chromium layer shows a significantly improved corrosion resistance.