• Restorative Dentistry and Endodontics
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• v.6 no.1
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• pp.115-122
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• 1980

The corrosion of silver amalgam is regarded as one of major causes in the failures of dental amalgam restorations. To evaluate the corrosion resistance of dental amalgam alloys, electrochemical tests such as potential and polarization measurement were used widely. But these commonly used methods have not provided the sufficient informations on relative resistance of amalgam to corrosion. In this experiment, the corrosion currents were measured using electronic potentiostat to compare some commercial dental amalgam alloys. All alloys were triturated in a amalgamator and condensed into a mold described in A.D.A. Specification No. 1 to produce cylinder form specimens of 4mm diameter by 5mm long. After specimen kept for 1 week at $37^{\circ}C$, each specimen was embedded in epoxy resin. The surfaces of specimens were then polished with a emery paper, diamond dust, and $Al_2O_3$. These specimens were immersed in artifical saliva kept at $37^{\circ}C$, and currents of each specimen were measured for 24 hours at 0.0volt (SCE). The author obtained conclusions as follows: 1. High copper amalgam showed superior resistance against corrosion to conventional amalgam, but a pellet form of high copper amalgam seemed to be susceptible to corrosion. 2. In lathe-cut alloys, fine-cut had superior resistance against corrosion to regular-cut. 3. Non-zinc conventional amalgam alloys were more resistant to corrosion than that of zinc containing conventional amalgam alloys. 4. In both of high copper and conventional amalgams, predispensed forms tended to have better resisitance to corrosion than that of pellet forms.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.38 no.5 s.118
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• pp.9-15
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• 2006

Wet compaction test (WCT) is a fiber evaluation method where wet fibers are compressed at one side of a cylinder and water drains out from the other side. The consistency of the fiber furnishes and their pressures are recorded during the test. In the previous study we found that WCT results always gave better coefficients of determination in fiber furnish drainage, and paper properties (density, tensile, tear, and burst strength) than those of WRV (water retention value). Fiber freeness and fiber length correlated well with drainage and tear strength of the furnishes, respectively; however, their correlations were very much improved by combining the WCT results. In this study, we used the WCT test for fractionated fiber furnishes to see whether improvement of the WCT is possible. We found that strength properties such as breaking length and burst index were correlated better with the fractionated long fiber furnishes. Drainage was greatly affected by the presence of short fiber furnishes. We used bleached chemical pulps (SwBKP, HwBKP), recycled pulp (OCC), and mechanical pulp (BCTMP) as fiber furnishes in this study. Fiber fractionation can be performed on-line in these days by using multifractor and WCT can be used as an on-line test in papermachine in the future.

• Advances in concrete construction
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• v.5 no.5
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• pp.539-561
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• 2017

In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

• Journal of Drive and Control
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• v.16 no.2
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• pp.8-14
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• 2019

A typical gantry crane is generally used to lift and transport objects in various workplaces. Most of the supporting structures in a gantry crane are fixed on the ground while the moving hoist is running overhead along the girder. There are some disadvantages to its long installation time and high installation cost. Therefore, a hydraulic based gantry crane was studied to solve the issues of typical gantry cranes. The supporting structure of the proposed gantry crane consisted of a hydraulic cylinder and telescopic boom. The dimension of the proposed gantry crane can be decreased due to its simplified structure. The analytical and theoretical methods were used to verify the structural stability of the proposed crane. The most severe load condition was considered for the analysis, and the stress and deflection of the structure are analyzed. The simulation results were as expected from the theoretical analysis. Finally, the structural and dynamic safety of the proposed hydraulic based gantry crane was validated. The obtained results can be used as guidelines in the design process of the hydraulic based gantry crane.

• The Journal of Advanced Prosthodontics
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• v.11 no.4
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• pp.232-238
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• 2019

PURPOSE. The aim of this study was to investigate simulated localized and generalized wear of indirect composite resins used for implant supported provisional restorations. MATERIALS AND METHODS. The study investigated ten indirect composite resins. Two kinds of wear were simulated by 400,000 cycles in a Leinfelder-Suzuki (Alabama) machine. Localized wear was simulated with a stainless-steel ball bearing antagonist and generalized with a flat-ended stainless-steel cylinder antagonist. The tests were carried out in water slurry of polymethyl methacrylate beads. Wear was measured using a Proscan 2100 noncontact profilometer in conjunction with Proscan and AnSur 3D software. RESULTS. Both localized and generalized wear were significantly different (P<.05) among the indirect composite resins. SR Nexco and Gradia Plus showed significantly less wear than the other indirect composite resins. The rank order of wear was same in both types of wear simulation. CONCLUSION. Indirect composite resins are recommended when a provisional implant-supported restoration is required to function in place over a long period. Although only some indirect composite resins showed similar wear resistance to CAD/CAM composite resins, the wear resistance of all the indirect composite resins was higher than that of bis-acryl base provisional and polymethyl methacrylate resins.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.101-107
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• 2019

This study conducted a simulation to observe the performance of a multi-turbocharged gasoline internal combustion engine for a high-altitude long-endurance unmanned aerial vehicle (HALE UAV). The WAVE 1-D engine simulation software from Ricardo was used for the engine system modeling and simulation. The specifications of a 2.4-L four cylinder gasoline engine from commercial vehicles and maps of commercial vehicle turbochargers were applied to the multi-stage turbocharged engine system model. Three turbochargers and intercoolers were installed in series for the appropriate intake of pressure for the gasoline engine at a high altitude of 60,000 ft. There was one wastegate for the turbochargers. The operability of the engine system was analyzed via this simulation model.

• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.4
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• pp.211-219
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• 2019

In this study, SMG(Smart Material with Grease) was developed, which was improved the precipitation minute particle in grease during long term standstill. Also, small-sized cylinder damper equipped with an electromagnet in a piston was developed for using a performance evaluation of the damper with SMG and the dynamic load test, and damping force using Power model and Bingham model was derived in order to compare to the result of that of the damper. The data obtained from the dynamic load test were analyzed and plotted, and then a dynamic range was calculated to evaluate the usability of the damper with SMG. The performance of the damper with SMG was compared to the damping forse derived from the Power and Bingham model. The result of this evaluation shown that the usability of SMG damper was demonstrated by this test as a semi-active controlling equipment of small-sized damper.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.11
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• pp.8-15
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• 2020

The government has announced its Hydrogen Economy Roadmap to strengthen global competitiveness on the hydrogen economy by focusing on hydrogen fuel cell electric vehicles and fuel cells. In this regard, the interest on the economics and safety of the infrastructure of hydrogen stations has also increased. In this study, a test bed similar to an actual hydrogen charging facility was built, and a prototype of a piston-type compressor was modeled. In this model, the piston was hydraulically compressed to progressively test leakage, leakage rate, and durability and to check for any malfunction. Moreover, the leakage rate, cylinder leak performance, and compressor operation durability were evaluated for safety; it was confirmed that there were no abnormalities. Nevertheless, an investigation of the long-term use and operating pressure of the compressor is necessary to verify the safety of developing a100-MPa domestic compressor in the future.

• Journal of Ocean Engineering and Technology
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• v.37 no.3
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• pp.89-98
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• 2023

Analyzing the interactions of free surface waves caused by a submerged-body movement is important as a fundamental study of submerged-body motion. In this study, a two-dimensional mini-towing tank was used to tow an underwater body for analyzing the generation and propagation characteristics of free surface waves. The magnitude of the maximum wave height generated by the underwater body motion increased with the body velocity at shallow submerged depths but did not increase further when the generated wave steepness corresponded to a breaking wave condition. Long-period waves were generated in the forward direction as the body moved initially, and then short-period waves were measured when the body moved at a constant velocity. In numerical simulations based on potential flow, the fluid pressure changes caused by the submerged-body motion were implemented, and the maximum wave height was accurately predicted; however, the complex physical phenomena caused by fluid viscosity and wave breaking in the downstream direction were difficult to implement. This research provides a fundamental understanding of the changes in the free surface caused by a moving underwater body.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.186-192
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• 1975

In the course of anthracite briquet combustion, air draft is usually controlled to continue burning of definite amount of briquet in the conventional hollow clay cylinder with air inlet hole open for given time, so that a large amount of CO tends to be produced. Therefore, it is necessary to establish an improved combustion process to depress the yielding rate of CO and for this purpose, we performed a basic experiment in which combustion rate of CO was measured in the mixture of $N_2, O_2 $and CO gas with or without the presence charcoal at the various temperature. The observed results showed that the burning temperature of CO is about 680${\sim}700^{\circ}C$, further burning rate of it was increased with increasing the amount of draft. From these facts, longer combustion time and low CO generation are thus contradictory to each other and it has been long desired to make those two compatible somehow. The purpose of the present investigation lies in designing an effective new briquet stove to meet the above requirements. The essential feature of the new briquet stove consisted in the use of two hollow iron cylinders with different inside diameter. A cylindrical air jacket thus formed served as a path through which small amount of secondary air run from the bottom of the stove to the upper vent holes. Heat exchange occurred between the upgoing secondary air and the burning briquet, which lowered the combustion temperature of the briquet. The results observed were selfevident as anticipated. It was confirmed that the combustion time was increased tolerably due to the heat loss from the combustion zone and that CO in the flue gas was reoxidized at the upper portion of the stove by the upgoing hot secondary air. By this reoxidation reaction the concentration of CO in the flue gas was found to be about 1/20 of that in case the conventional clay cylinder was used as briquet jacket.