• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.652-655
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• 2003

In this paper, step-down piezoelectric transformer is studied. The piezoelectric transformer, made of lead zirconate titanate solid solution ceramic, is operated by a fundamental contour-extensional vibration mode. The transformer of 14mm length, 14mm width and 4.5mm thickness was made up two shape(Type I and II). The resonant frequency (fr) is 144kHz and 128kHz at the load resistant of $7.5{\Omega}$ that is a similar to calculating matching impedance. The gain (G) obtained 0.19 and 0.08 at each resonant frequency, when applied input voltage is 25V. The temperature difference with the variation of load resistant was increased with increasing load resistant and was the lowest at $7.5{\Omega}$ near the matching of output impedance.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.365-370
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• 1998

The creep strain of the compression zone of concrete beams subjected to cyclic loading should be a significant factor in increasing strain and deflections. An analytical model which is similar to a previous one is presented to predict the increase in cyclic creep strain and the damage using the properties of the constituent materials: concrete and steel. The analytical expressions are compared with our experimental data. The effect of concrete-creep is accounted by the term En, Icr,n, and Mcr,n. In this study, it is proved that cyclic creep exponents 'n' in Cyclic Creep Model, according to the parameters -strength, range of stress- have the various values. It is hoped that with the availability of more experimental data and better understanding of some of the complex behavior, the model could be further improved.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.771-777
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• 2007

In this paper, thermal expansion coefficients of fiber-reinforced composite materials are predicted by direct numerical simulation. From comparing the predicted results with experimental results, it is confirmed that direct numerical simulation gives similar results to the previously proposed methods while minimizing artificial assumptions. Additionally trend of variation in thermal expansion coefficients is investigated according to the fiber volume fraction.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.265-270
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• 2003

When designing an engine part the designer has to choose the proper material and to define the dimensions of the part. in the most rudimentary case he has available as guidelines the collective experience from similar applications. The performance of the part is tested on occasion of the trial runs for the full system, and possibly occurring deficiencies are corrected until a satisfactory usable life and safety of operation is achieved. This procedure is time consuming and costly, and the learning effect is minimal. These requirements have to be condensed into characteristic values ameanable to computation. Since testing and computation are complementary we have to look at the currently existing mathematical models for engine bearing performance.

• Journal of the Korean Society for Precision Engineering
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• v.8 no.4
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• pp.33-40
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• 1991

The decrease in surface roughness of work roll and steel strip in cold rolling of low carbon steel strip has been investigated by working distance, materials, total separating force and total reduction ratio. The main results are as follows; For the same lubricating conditions. 1) The changing of surface roughness of steel strip were similar to work roll. The transcription ratio is in inverse proportion to the carbon content of steel strip. 2) The surface roughness of steel strip is hardly change according to changing of total separating force and total reduction ration. 3) The wear of work rolls surface is more rapid in that case of continuous casted steel strip than ingot casted steel strip. The aluminium content dull powder adhere on the rolls surface, and so. It makes the mirror surface of work roll accelerate.

• ALGAE
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• v.22 no.3
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• pp.159-165
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• 2007

Morphological and anatomical characters of Amphiroa rigida Lamouroux were investigated with field materials and taxonomic accounts are given to the species. The species grows in the subtidal zone of Cheju island, and is characterized by semiendophytic habit in Hydrolithon onkodes. The species is well defined by about 1 cm height, loosely tufted thallus with irregular branches, two-tiered geniculum with equal length, geniculum tier connecting by oblique end walls, and conceptacles buried in cortices of intergeniculum. Korean isolates have etrasporangial, male and female conceptacles. The structure and developmental patterns of conceptacles are very similar to those shown in previous studies.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.5
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• pp.31-38
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• 2016

This study proposes an optimal design for a robotic welding system for a high-strength steel armor plate. In order to identify the welding defect parameters, we analyzed the 4M (man, machine, materials, method) characteristics diagram, as well as a cause and effect matrix, to improve the productivity and quality of welding defects. From these analyses, we designed optimal welding conditions and carried out welding tests -- such as mechanical testing and macro structure tests - with positive results. We determined that it was possible to obtain a quality similar to manual welding with our robotic welding system. In the future, we expect that the system will be used as inspiration for future welding system designs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.289-294
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• 2001

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear phenomena.

• Laser Solutions
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• v.2 no.1
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• pp.61-67
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• 1999

This study introduces the new concept in the evaluation criteria of the $CO_2$ laser Tailored Blank weldability, The materials used are 0.7mm, 1.5mm thick low carbon automotive galvanized steels. Welding tests were conducted for both similar thickness(0.7mm-0.7mm, 1.5mm-1.5mm) and dissimilar thickness(0.7mm-1.5mm) cases. The criteria developed for optimum welding conditions were based on relationship between results of die press forming test, weld transverse tensile test Erichsen test and weld penetration measurements. Application of the developed criteria(fracture ratio, strength ratio and D/To) in obtaining optimum welding condition revealed that a weld which satisfied any of the criteria did not fracture during actual die press test.

• Journal of Life Science
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• v.6 no.4
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• pp.299-303
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• 1996

The effects of ozone (O$_{3}$) exposures on chlorophyll content of trembling aspen(Populus tremuliodes) rooted cuttings were studied. Ozone was treated with 100 ppb fumigation for 6 hours per day, for three consecutive days per week in open-top chamber. The ozone exposures caused severe foliage damage expressed in necrotic patches and extensive chlorosis. Degradation of chlorophyll was observed mostly in mature leaves. The chlorophyll response to ozone exposure maintained a similar pattern during all experimental seasons and plant materials, Significant genetic variation in O$_{3}$ responses was revealed by differences in sensitivies among clones.