• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.64-64
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• 2009

Atomic force microscopy (AFM) fabrication of oxide patterns is an attractive technique for nanoscale patterns and related device structures, SiC exhibits good performance in high-power, high-frequency, and high-temperature conditions that is comparable to the performance of Si. The AFM fabrication of oxide patterns on SiC is important for electronic applications. However, there has not been much reported investigations on oxidation of SiC using AFM. We achieved the local oxidation of 4H-SiC using the high loading force of ~100 nN, although the oxidation of SiC is generally difficult mainly due to the physical hardness and chemical inactivity. All the experiments were performed using atomic force microscopy (S.I.S. GmbH, Germany) with a Pt/Ir-coated Si tip at ~40% humidity and room temperature. The spring constant and resonance frequency of the tip were around ~3 N/m and ~70 kHz. We fabricated oxide patterns on n-type 4H-SiC ($\sim10^{19}/cm^3$) and n-type Si ($\sim1.9\times10^{16}/cm^3$). In summary, we demonstrated that the oxide patterns can be obtained over the electric field of ${\sim}\times10^7 V/cm$ and the high loading force using the tip as a cathode. The electric field transports the oxyanions (OH-) to the positively biased surface.

• Journal of Korean Society of Water and Wastewater
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• v.11 no.1
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• pp.33-41
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• 1997

An attempt was made to enhance anaerobic treatment efficiency by adopting the anaerobic sequencing batch reactor(ASBR) process at a thermophilic temperature. Operational characteristics of the ASBR process were studied using laboratory scale reactors and concentrated organic wastewater composed of soluble starch and essential nutrients. Effects of fill to react ratio (F/R) were examined in the Phase I experiment, where the equivalent hydraulic retention time(HRT) was maintained at 5 days with the influent COD of 10g/L. A continuous stirred tank reactor(CSTR) was operated in parallel as a reference. Treatment efficiency was higher for the ASBRs because of continuous accumulation of volatile suspended solids(VSS) compared to the CSTR. However, the rate of gas production and organic removal per unit VSS in the ASBRs was much lower than the CSTR. This was caused by reduced methane fermentation due to accumulation of volatile acids(VA), especially for the case of low F/R, during the fill period. When the F/R was high, maximum VA was low and the VA decreased in short period. Consequently, more stable operation was possible with higher F/R. Effects of hydraulic loading rate on the efficiency was studied in the Phase II experiment, where the organic loading rate was elevated to 3333mg/L-d with the F/R of 0.12. Reduction of organic removal along with rapid increase of VA was observed and the stability of reaction was seriously impaired, when the influent COD was doubled. However, operation of the ASBR was quite stable, when the hydraulic loading rate was doubled and a cycle time was adjusted to 12 hour. It is essential to avoid rapid accumulation of VA during the fill period in order to maintain operational stability of the ASBR.

• Corrosion Science and Technology
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• v.3 no.5
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• pp.216-221
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• 2004

The operating experience showed that the fatigue is one of the major piping failure mechanisms in nuclear power plants (NPPs). The pressure and/or temperature loading transients, the vibration, and the mechanical cyclic loading during the plant operation may induce the fatigue failure in the nuclear piping. Recently, many fatigue piping failure occurred at the socket weld area have been widely reported. Many failure cases showed that the gap requirement between the pipe and fitting in the socket weld was not satisfied though the ASME Code Sec. III requires 1/16 inch gap in the socket weld. The ASME Code OM also limits the vibration level of the piping system, but some failure cases showed the limitation was not satisfied during the plant operation. In this paper, the fatigue behavior of the socket weld in the nuclear piping was estimated by using the three dimensional finite element method. The results are as follows. (1) The socket weld is susceptible to the vibration if the vibration levels exceed the requirement in the ASME Code OM. (2) The effect of the pressure or temperature transient load on the socket weld in NPPs is not significant because of the very low frequency of the transient during the plant lifetime operation. (3) 'No gap' is very risky to the socket weld integrity for the specific systems having the vibration condition to exceed the requirement in the ASME OM Code and/or the transient loading condition. (4) The reduction of the weld leg size from $1.09*t_1$ to $0.75*t_1$ can affect severely on the socket weld integrity.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.E2
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• pp.74-81
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• 2007

Feasibility test for a biofilter was performed to treat VOCs. The applied loading rate to the biofilter was calculated between 60 to $3,700\;kg\;COD/m^3$. Trimethyl-pentene and trimethyl-hexene were the two most dominant compounds and they occupy about 85 percent. During the acclimation period, it is desirable for a biofilter to receive relatively lower VOCs concentration and flow rate, until it can adjust to new substrate and operational environment. Temperature at various points inside the biofilter reactor was observed with more than 23 temperature sensors. With steam heating, temperatures of the top sections of the media were greater than those of bottom sections. Without steam heating, intermediate stages generally had higher temperature measurement than those of bottom and top stages. Because the pH values for different biofilter materials vary significantly, measurement of the pH for the mixture of different combinations of biofilter materials is necessary. Based on the types and brands of media, the measured pH ranged from 5.38 to 9.10. The range of measured pH of different mixtures with perlite, compost, saw dust, peat moss, limestone, vermiculite was 7.05 to 8.62.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2205-2213
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• 1993

The characteristic test for gage factors of temperature self-compensated strain gages at cryogenic temperature is presented. By joining the international round robin test on electrical strain gages at cryogenic temperatures, the gage factors of three kinds of widely-used strain gages are obtained at the room temperature, the temperatures of liquid nitrogen and liquid helium. The calibration system which produce precise bending strain is by mechanical loading at cryogenic temperature. This paper also presents the creep characteristic of strain gages at maximum strain level.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1781-1791
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• 1991

For the cracked plate under transient temperature distribution, J-integral is expressed in the form of line integral by using convolution integral. The J$_{1}$ integral is calculated for a through line center cracked steel plate under thermal and mechanical loading conditions and the calculated values are in good agreement with previous results. The effect of inertia term on the J$_{1}$ integral is not negligible for a glass but for a steel. For the glass plate, the rates of J$_{1}$ integral value to time increase if the values of material properties such as specific heat, thermal conductivity, thermal diffusivity and Young`s modulus as well as crack length and temperature difference in cracked edge increase.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.409-412
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• 2006

Bulk metallic glass (BMG) strips of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ were produced by warm rolling of the amorphous powder canned with copper. Controlling of temperatures of the rolled sample and rolls was essential for the successive rolling process. Because improper controlling of the sample temperature gave rise to the crystallization of BMG loading to the catastrophic fracture of BMG strips, the temperature of rolls should be properly controlled for achieving successful powder rolling of BMG. The variations of the strain state and temperature in the roll gap was simulated by the finite element method(FEM) using various roll temperatures.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.11
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• pp.559-567
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• 2002

This paper presents the general recommendations for the overload criterions of mineral-oil-immersed distribution transformers rated 100kVA and less. For this purpose, we analyze the characteristics of top-oil temperature rising for mineral-oil-immersed power distribution transformer rated 100kVA and less, manufactured in Korea, In order to analyze the characteristics of top-oil temperature rising due to the distribution transformer loading, we performed experiments at KERI (Korea Electrical Research Institute) from December 2000 to May 2001. The restraint of ambient temperatures for the experiment results is solved using the results of foreign standards. Finally, we present the overload criterions of distribution transformer for summer and winter season, respectively.

• Carbon letters
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• v.9 no.4
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• pp.283-288
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• 2008

The composites of temperature-sensitive hydrogel and activated carbons were prepared in order to improve both the mechanical strength of hydrogel matrix and the loading capacity of drug in a hydrogel drug delivery system. The swelling of composite hydrogel was varied depending on the temperature. Both the swelling and the release behavior of the composite hydrogel were varied depending on the kind of activated carbon. The release behavior showed the high efficiency which is important for practical applications.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.441-446
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• 2000

Although the net-shape molding of composites is generally recommended, molded composites frequently required cutting or grinding due to the dimensional inaccuracy for precision machine elements. During the composite machining operations such as cutting and grinding, the temperature at the grinding area may increase beyond the allowed limit due to the low thermal conductivity of composites, which might degrade the matrix of composite. Therefore, in this work, the temperature at the grinding point during surface grinding of carbon fiber epoxy composite was measured. The grinding temperature and surface roughness were also measured to investigate the surface grinding characteristics of the composited. The experiments were performed both under dry and wet grinding conditions with respect to cutting speed, feed speed, depth of cut and stacking angle. From the experimental investigation, the optimal conditions for the composite plain grinding were suggested.