• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.272-272
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• 2008

Diamond-like carbon (DLC) 박막은 높은 경도, 내 마모성, 화학적 안정성, 전기적 절연성, 높은 광 투과성을 가지고 있어, 공구강, 광학렌즈 및 플라스틱의 보호 코팅을 위해 응용되어진다. 하지만, DLC 박막은 높은 잔류응력으로 adhesion이 떨어진다는 단점이 있다. 따라서 본 연구에서는 전처리가 13.56MHz 150W RF플라즈마 화학기상 증착(RF-PECVD) 법을 통한 DLC 박막의 합성에 어떤 영향을 미치는지 알아보기 위해, $H_2$ (80 sccm), $O_2$ (10 sccm), $N_2$ (20 sccm)의 다른 가스를 사용하여 전처리를 하였다. DLC 박막 합성 후, 특성은 Raman, scratch test, contact angle 등의 측정을 통하여 분석되었다.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.373-378
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• 2000

The crevice corrosion of local corrosion occur when the gap exist on metal surface. This crevice corrosion happen to region such as flange of pipe, contact part of casing, under gasket and packing, between valve disk and seat of pump etc. Especially The crevice corrosion of mild steel(SS 400) get serious. This paper was studied on the crevice corrosion of SS 400 in fluid environment. In $0\%,\;2\%,\;3.5\%,\;5\% NaCl$ solution, the aspect of the crevice corrosion and polarization behavior under the crevice corrosion was investigated. And Weight loss rate of SS 400 with crevice and non-crevice was measured according to the NaCl concentration. The main results obtained are as follows : 1) Under crevice corrosion, the corrosion potential become less noble as the concentration of NaCl solution increased. 2) The current density under open circuit potential was high drained as concentration of NaCl solution increased by $3.5\%$ but the concentration increased over $3.5\%$, the current density was low drained. 3) The weight loss rate of SS 400 was increased as concentration of NaCl solution Increased by $3.5\%$, but the concentration increased over $3.5\%$, that of SS 400 was decreased. 4) Effect of oxygen for crevice corrosion in the concentration of $3.5\%$ NaCl solution become sensitive than that $0\%$ NaCl solution.

• JSTS:Journal of Semiconductor Technology and Science
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• v.5 no.2
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• pp.113-119
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• 2005

4H-SiC planar MESFETs were fabricated using ion-implantation on semi-insulating substrate without recess gate etching. A modified RCA method was used to clean the substrate before each procedure. A thin, thermal oxide layer was grown to passivate the surface and then a thick field oxide was deposited by CVD. The fabricated MESFET showed good contact properties and DC/RF performances. The maximum oscillation frequency of 34 GHz and the cut-off frequency of 9.3 GHz were obtained. The power gain was 10.1 dB and the output power of 1.4 W was obtained for 1 mm-gate length device at 2 GHz. The fabricated MESFETs showed the charge trapping-free characteristics and were characterized by the extracted small-signal equivalent circuit parameters.

• Journal of Electrochemical Science and Technology
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• v.5 no.4
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• pp.95-104
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• 2014

Electrochemical performance of Li-ion cells with $LiMn_2O_4$ cathodes and graphite anodes with carbonates electrolytes containing quaternary ammonium-based room temperature ionic liquids (ILs) is investigated. Eight different ILs based on tetraalkylammonium, pyrrolidinium or piperidinium cations paired with bis(trifluoromethylsulfonyl)imide or tris(pentafluoroethyl)trifluorophosphate anions are examined in combination with dimethyl carbonate as a main solvent and fluoroethylene carbonate as a solid electrolyte interface forming agent. It is shown that cycling properties of the cells are strongly affected by the content of ILs in the electrolyte mixtures and its increase corresponds to lower discharge capacity retention. Since viscosity and conductivity of ILs are of a great importance for the electrolytes formulation, some kind of combined parameter should be used for the assessment of IL applicability and calculated values of Walden products for neat ILs represent one of the possible options. Besides, positive effect of ILs on reduction of flammability and enhancement of thermal stability of electrolytes in contact with charged electrodes have been demonstrated by means of self-extinguishing time test and differential scanning calorimetry respectively.

• Journal of Environmental Health Sciences
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• v.13 no.2
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• pp.51-63
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• 1987

We identified pyrolysis condition, effect of catalyzer and pyrolysis mechanism through contact decomposed method by adding Bentonite in waste plastic of hospital solid waste. The result from this study were summarized as the followings: 1. The optimum fuel oil were obtained when hospital wasted plastic (P.P) and Bentonite were mixed in the ratio of 30:1. 2. Maximum absorption wave of hospital wasted plastic (P.P) appeared at 2900cm$^{-1}$, 1480cm$^{-1}$, 1360cm$^{-1}$ and 1180 cm$^{-1}$ by FT-IR and the plastics were identified and confirmed. 3. Reaction temperature of hospital wasted plastic started at 360$\circ$C, proceed rapidly at 437.5$\circ$C and finished at 481$\circ$C. The residue was 0.729%. When bentonire was added started at 318$\circ$C, proceed rapidly at 399.5$\circ$C and finished at 449.3$\circ$C, the residue being 4.23%. 4. Pyrolysis products of hospital wasted plastic were about 90 kinds. The Main components were 2-Heptene-3-ethyl-4-trimethyl (27.4%), 1-Heptene-2-isobutyl-6-methyl (8.6%) and 1-Heptene decene (7.7%). There was little component difference at different temperature. This is the result from stability of decomposition product. 5. Pyrolysis efficiency increased by the addition Bentonire. 6. Some of the Environmental and Sanitary problems could be solved by the pyrolysis of hospital wasted plastic and the decomposed products were to be used as fuel oil.

• Journal of the Korean Home Economics Association
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• v.45 no.7
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• pp.71-91
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• 2007

We investigated the ecological variables of adolescent sexual behavior. We grouped the behaviors into organism, microsystem, mesosystem, and exosystem. The variables belonging to the organism group were sexual attitude, sex, grade, sexual knowledge, sexual education, dating experience, problem behaviors, and self-control. The microsystem variables included the parent-adolescent communication about sexuality, parental monitoring, parent educational background, friend relationships, and school environment. Moreover, the mesosystem variables included family-peer and family-school relationships. The exosystem variables were comprised of neighborhood environment and pornography. The study group included 369 adolescents from the first and second grade of several high school in Daegu, Korea. We found that the factors affecting adolescent sexual behavior included grade, sex, dating experience, self-control, smoking, and pursuing sexual pleasure. As well, contact with deviant friends, father-adolescent communication about sexuality, school type, and attachment to teacher. In addition the family-peer relationship also affected adolescent's sexual behaviors as well as pornography and neighborhood environment. Lastly the variable belonging to the organism group was found to have the greatest effect on adolescent, sexual behavior compared to the other variables.

• Journal of The Korean Astronomical Society
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• v.44 no.3
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• pp.97-108
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• 2011

The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of $5.62{\times}10^{-8}$ day/yr, which can be interpreted in terms of mass transfer at a rate of $-4.38{\times}10^{-8}M_{\odot}$/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.100-103
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• 2004

In this work, the effects of oxy-fluorination on surface characteristics of carbon fibers were investigated in mechanical interfacial properties of carbon fibers-reinforced composites. The surface properties of the carbon fibers were determined by X-ray photoelectron spectroscopy (XPS), FT-IR. and contact angle measurements. And their mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical stress intensity factor $(K_{IC})$. As experimental results, the $F_{1S}/C_{1S}$ ratio of carbon fiber surfaces was increased by oxy-fluorination, due to the development of the oxygen containing functional groups. The mechanical interfacial properties of the composites, including ILSS and $K_{IC}$, had been improved in the oxy-fluorination on fibers. These results could be explained that the oxy-fluorination was resulted in the increase of the adhesion between fibers and matrix in a composite system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.489-496
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• 1988

This paper is studied to know wear mechanism in variation of austempering temperature and holding time of austempered ductile cast iron against mating material SM45C hardened by heat treatment. The wear tests were carried out by rubbing the annular surface of two test pieces in dry sliding friction. The wear mechanism was investigated by scanning electron microscopy and the retained austenite volume fraction was investigated by X-ray diffractometer. The experimental results show that the wear characteristics depend largely on the oxidation of the testing materials which is influenced by the sliding velocity and distance. The retained austenite has a negative effect during frictional contact because it has increased severe wear by softened surface layer. It is shown experimentally that hard metals have lower frictional resistance and hence the resistance to adhesion is increased due to stronger interatomic linking bonds and increase in the surface energy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2647-2655
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• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).