• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.13-20
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• 2005

Micro EDM process is generally used for machining microholes, cavities, and three dimensional shapes. For machining micro structures, first of all, micro tool electrode is indispensable and WEDG system is proposed for tool fabrication method. When using WEDG, its machining characteristics are highly affected by many EDM parameters such as applied voltage, current, rotation speed, capacitance, and pulse duration. Therefore, the design of experiment is introduced to fully understand the effect of the EDM parameters on machining tool electrode. And an attempt has been made to develop the mathematical model for predicting the size of the tool electrode by calculating spark distance. The suggested model was verified with experiment and predicted working gap distance is in good accord with the measured value.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.180-182
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• 1994

In an electron storage ring of Pohang Light Source (PLS), electrons lose their energy in every turn by the synchronous radiation. A high power RF amplifier is employed to compensate the electron energy that is lost by the synchronous radiation. The specification of RF amplifier is an continuous output power of 60 kW at 500.082 MHz operating frequency. The power is supplied to RF cavities in the storage ring tunnel. Total number of amplifier system currently required is three. Tile total number will be increased upto five as the operating condition of storage ring is upgraded. The RF amplifier is mainly consisted of a high voltage DC power supply, an intermediate RF power amplifier (IPA), and a klystron tube. In this article, the design of RF amplifier system and characteristics of the klystron tube will be discussed.

• Restorative Dentistry and Endodontics
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• v.4 no.1
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• pp.17-21
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• 1978

The histopathological study was made to investigate the pulp reaction of "Hipol". The toxicity against the pulp tissue was compared with the "Zinc-Oxide-Eugenol Cement." A total of 36 cavities of healthy prmanent teeth of the 3 dogs were chosen and filled with the experimental filling materials without base. The teeth were prepared at 3 intervals; a week and two, three weeks as a result of this study. 1) Both "Hipol" and "Adaptic" showed very severe to moderate pulp reactions in the all of the filled teeth. 2) There was little difference between "Hipol" and "Adaptic" in the severity of the pulp reaction. 3) After 3 weeks, the teeth filled with "Hipol" and "Adaptic" showed more or less recovery phenomena. The teeth filled with "Zinc-Oxide-Eugenol Cement" showed marked recovery phenomenon. 4) There was little difference in the histopathological result between "Universal" group and "Catalyst" group.

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.617-617
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• 2003

I. Objectives This study was done to evaluate whether or not there are any differences in microleakage of the class 5 composite restoration that were filled at the smooth surface and the proximal surface respectively. In addition any differences between small and large-sized restoration were also studied. II. Materials and Methods Total sixty-four class 5 resin restorations, sixteen per group, were made in the permanent teeth. Two-sized cavities, small ($2{\;}{\times}{\;}2{\;}{\times}{\;}1.5{\;}mm$) and large ($4{\;}{\times}{\;}2{\;}{\times}{\;}1.5{\;}mm$), were filled at the smooth surface and the proximal surface each.(omitted)

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.571-571
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• 2003

Composite inlays are indicated for large cavities and different approaches have been proposed to improve the adaptationof Class II restorations, including applying base. The purpose of this study was to compare in vitro the marginal adaptation of class II(MOD) composite inlays(Tescera ATL system, Bisco) made with or without bases, having different physical properties. Extracted human lower molars were used for this study. The base was made from Aeliteflo(Bisco), Dyract AP(Bisco) or Fuji II LC improved(GC) respectively and the comtrol group has no base.(omitted)

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.574-574
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• 2003

I. Objectives Newly all-in-one adhesives were developed for reducing the techique sensitivity and chair time, but lots of concerns were made on bondability, longevity, and microleakage. The object of this study was to measure micro leakage and marginal quality of all-in-one adhesives using electrochemical method and SEM analysis quantitatively. II. Materials and Methods After making Class V cavities, they were bulk filled with Heliomolar(＃A1) after surface treatment with three adhesives：Adper Prompt (Group 1), One up bond F (Group 2), Xeno III(Group 3).(omitted)

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.447-453
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• 2009

The interior noise of the High Speed Train(HST) is analyzed by applying the statistical energy analysis (SEA) method. The interior of each vehicle is divided lengthwise into nine cavities. Since the rolling noise and aerodynamics noise are expected to be dominant noise sources, they are treated as the noise sources in the model. To further simplify the model, curtains and seats are excluded. The simulation runs involving one-car, three-car and five-car trains are conducted. The maximum predicted noise level is 98.4dB. The results also show that the predicted noise levels are within 0.23% of each other. The results imply that it is not necessary to estimate the interior noise of the train by constructing multiple-car train models. The noise estimate based on just one-car train can be optimal with respect to the computational effort and modeling time.

• Nuclear Engineering and Technology
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• v.41 no.9
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• pp.1205-1214
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• 2009

The critical heat flux (CHF) levels that occurred due to exponential heat inputs for varying periods to a 1.0-mm diameter horizontal cylinder immersed in various liquids were measured to develop an extended database on the effect of high subcoolings for quasi-steady-state and transient maximum heat fluxes. Two main mechanisms of CHF were found. One mechanism is due to the time lag of the hydrodynamic instability (HI) which starts at steady-state CHF upon fully developed nucleate boiling, and the other mechanism is due to the explosive process of heterogeneous spontaneous nucleation (HSN) which occurs at a certain HSN superheat in originally flooded cavities on the cylinder surface. Steady-state CHFs were divided into three regions for lower, intermediate and higher subcooling at pressures resulting from HI, transition and HSN, respectively. HSN consistently occurred in the transient boiling CHF conditions that correspond to a short period. It was also found that the transient boiling CHFs gradually increased, then rapidly decreased and finally increased again as the period became shorter.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.569-575
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• 2018

The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

• Transactions of Materials Processing
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• v.22 no.1
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• pp.17-22
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• 2013

Tube hydroforming is a technology that utilizes hydraulic pressure to form a tube into desired shapes inside die cavities. Due to its advantages, such as weight reduction, increased strength, improved quality, and reduced tooling cost, single-layered tube hydroforming is widely used in industry. However in some special applications, it is necessary to produce multi-layered tubular components which have corrosion resistance, thermal resistance, conductivity, and abrasion resistance. In this study, a hollow forming process to fabricate a part from multi-layered tubes for structural purposes is proposed. To accomplish a successful hydroforming process, an analytical model that predicts optimal load path for various parameters such as tube material properties, thickness of tubes, diameter of holes and the number of holes was developed. Tubular hydroforming experiments to fabricate a hollow part were performed and the optimal loading path developed by the analytical model was successfully verified. The results show that the proposed hydroforming process can effectively produce hollow parts with multi-layered tube without defects such as wrinkling or fracture.