• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.430-439
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• 1990

Steady state turbulent airflow and unsteady characteristics of generation, transportation, and recovery behavior of contaminate particles in the simplified 2 dimensional Vertical Laminar Flow (VLF) type clean room was numerically simulated using the low Reynolds number k-over bar.epsilon- turbulent model. Characteristics of airflow in VLF type clean room are greatly affected by the recirculation zone around working surface. The recirculation zone must be considered at the time of clean room design because the recirculation zone whose area increases with increment of inlet velocity exerts bad influence upon the performance of clean room in terms of particle contamination. The location of maximum particle concentration changes from the location of particle source to the recirculation zone, while averaged particle concentration is reduced exponentially with time. Recovery time of clean room with spontaneous particle generation source is inversely proportional to inlet velocity. We introduce nondimensionalized recovery time through the dimensional analysis, which can indicates the general performance of clean room with design structure change. It was identified that .tau. is independent of inlet velocity and background concentration. Therefore .tau. can be the simple factor to compare the different structure of clean room in terms of dynamic response to contamination and becomes larger with better structure of clean room.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.240-240
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• 2010

A multiple alloy metal nano-dots memory using FN tunneling was investigated in order to confirm its structural possibility for future flash memory. In this work, a multiple FePt nano-dots device with a high work function (~5.2 eV) and extremely high dot density (${\sim}\;1.2{\times}10^{13}/cm^2$) was fabricated. Its structural effect for multiple layers was evaluated and compared to one with a single layer in terms of the cell characteristics and reliability. We confirm that MOS capacitor structures with 2-4 multiple FePt nano-dot layers provide a larger threshold voltage window and better retention characteristics. Furthermore, it was also revealed that several process parameters for block oxide and inter-tunnel oxide between the nano-dot layers are very important to improve the efficiency of electron injection into multiple nano-dots. From these results, it is expected that a multiple FePt nano-dots memory using Fowler-Nordheim (FN)-tunneling could be a candidate structure for future flash memory.

• International Journal of Industrial Entomology and Biomaterials
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• v.33 no.2
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• pp.50-53
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• 2016

The size of head capsule is one of the most important factors for identifying developmental stage. In order to understand the developmental characteristics of the butterfly Atrophaneura alcinous, we examined fluctuations in larval head capsule size under three different temperature conditions (20, 25, and $30^{\circ}C$) and 60% humidity. As a result, larvae developed to the fifth instar at all three temperatures. The head capsule size of larvae tended to be larger at the lowest temperature and smaller at the highest temperature. The development rate showed a regular change, consistent with Dyar's rule regarding head capsule size development. Furthermore, the development of head capsule size was found to correspond to a second degree polynomial regression better than to a linear regression. On the basis of these results, it would appear to be possible to perform an accurate assessment of instar status during the development of A. alcinous.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.484-491
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• 1990

A heat-flux meter has been designed and manufactured to measure the heat flux from the flame. A calibration method of the heat-flux meter by a calibration furnace has also been proposed. The k-type (Chromel-Alumel) thermocouple material has been used as the material for the beat-flux meter. The electormotive force (e.m.f.) from the K-type thermocouple is shown to be linearly proportional to the heat flux absorbed. The characteristics of the heat-flux meter become better as the radius of heat absorbing disk becomes larger and its thickness thinner.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.893-900
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• 1994

In this study, workspace analysis has been performed for a Clemens Coupling type parallel robotic wrist with four degrees of freedom such as three angular degrees of freedom and 1 plunge motion. Because of plunge motion, this mechanism has no singular point that the general roll-pitch-roll mechanisms have. Also, proposed mechanism performs larger load, faster motion, with less weight and has better structural characteristics such as higher stiffness and strength to weight ratio compared with serial type mechanisms. As a basic step for position control, the closed form solution of forward and inverse kinematics are proposed and workspace is analyzed and plotted by applying triangle tracer method for workspace boundary tracing.

• Journal of the Korean Institute of Educational Facilities
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• v.13 no.2
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• pp.50-60
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• 2006

In search of the improvement plan for elementary schools which aims at the efficient application of new educational programs according to the introduction of the 7th National Curriculum, the analysis results for the spatial configuration regarding the modernized elementary schools in Busan City are as follows: 1) The analysis of expansion in the building area reveals that the building area per classroom has been increased from $200m^2$ in 1995 to $350m^2$ in 2005 based on the data gathered from the constructed schools during that period. 2) While the ratio of classrooms per the gross school area has been decreased from 35% in the late 1990s to 20% in the 2000s, the entire school size continue to become larger, which is considered as desirable change. 3) New construction and addition of special classrooms and multi-purpose spaces have continued to be increased. Multi-purpose spaces were positively considered in the early 2000s, but recently built schools tend to limit the construction of multi-purpose spaces only to lower grades' space or not to obtain them owing to the analysis that its utilization is limited. 4) Most schools constructed after 1999 are equipped with dining hall and multi-purpose halls, and show the increase in their sizes. Especially, dining hall tend to be located on the upper floors for better environmental conditions.

• Speech Sciences
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• v.8 no.2
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• pp.39-48
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• 2001

The purpose of this study was to examine changes in acoustic characteristics after drinking alcoholic beverages and singing in order to establish guidelines for vocal hygiene of both singers and non-singers. 21 university students (10 males and 11 females) vocalized /a/ before drinking, after drinking and after singing. Changes in vocal range and acoustic characteristics were analyzed by Dr. Speech 4.0 (Tigers Electronics). No significant difference was observed in vocal range following drinking. However, there was statistically significant changes in vocal range after singing. We may infer that appropriate amount of singing functioning as vocal warm-up, rather than drinking alone, resulted in improvement in their abilities to lengthen vocal folds. This is directly related to the ability to produce high-pitched sounds. Changes in jitter in female voices after singing was the only acoustic factor that was significant. Changes in Shimmer and NNE was not significant either after drinking nor singing. Subjects who were judged to perform better in singing were marked by minimum acoustic changes, which may due to their well-trained vocal fold function. The results of this study may address the necessity for vocal function exercises for the patients with neurogenic voice disorders including dysarthria. The need for more extensive research with a larger number of subjects including professional voice users is also addressed.

• Earthquakes and Structures
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• v.7 no.4
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• pp.463-484
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• 2014

Solid piers with a rounded rectangular cross-section are widely used in railway bridges for high-speed trains in China. Compared to highway bridge piers, these railway bridge piers have a larger crosssection and less steel reinforcement. Existing material models cannot accurately predict the seismic behavior of this kind of railway bridge piers. This is because only a few parameters, such as axial load, longitudinal and transverse reinforcement, are taken into account. To enable a better understanding of the seismic behavior of this type of bridge pier, a simultaneous influence of the various parameters, i.e. ratio of height to thickness, axial load to concrete compressive strength ratio and longitudinal to transverse reinforcements, on the failure characteristics, hysteresis, skeleton curves, and displacement ductility were investigated. In total, nine model piers were tested under cyclic loading. The hysteretic response obtained from the experiments is compared with that obtained from numerical studies using existing material models. The experimental data shows that the hysteresis curves have significantly pinched characteristics that are associated with small longitudinal reinforcement ratios. The displacement ductility reduces with an increase in ratio of axial load to concrete compressive strength and longitudinal reinforcement ratio. The experimental results are largely in agreement with the numerical results obtained using Chang-Mander concrete model.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.317-324
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• 2010

Marine transportation by ships is characterized by remote, large-volume and lower rates than the others carry system. Ships account for over 80% of all international trading, and marine transportation is an internationally competitive, strategic, and great national important industry. The construction of larger and faster ships has brought about many problems such as cavitations and erosion corrosion. Cavitations and erosion corrosion make damages on materials and leads to break down members due to continuous physical contacts with shock waves and fluids from the generation and extinction of air bubbles in sea water vortex. The steel used for ship constructions was spray-coated with Al wire, and additionally sealed with fluorine silicone sealing material. Results of experiment, corrosion resistance of sealed thermal spray coating was improved, however in cavitation resistance, the large effect was not appeared. Accordingly, this study applied for thermal spray coating to provide better electrochemical characteristics and corrosion resistance in marine environment.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.33 no.3
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• pp.9-17
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• 2001

The floc characteristics of base paper stock for coating by the retention aid system consisting of polyacrylamide (high molecular weight low charge density, HMLC) and PEI without and with anionic inorganic oxide (IO) were investigated under various shear conditions of MDDA (modified dynamic drainage analyzer). The floc size was increased with cationic electrolytes dosage whatever inorganic oxide is applied or not. The effect of inorganic oxide on the floc size showed the different result between PAM and PEI. The smaller floc was obtained by PAM without inorganic oxide, but larger floc was obtained by PAM with inorganic oxide. However, the effect of shear force was not observed. Floc formation index was decreased by the addition of cationic electrolytes with or without inorganic oxide. Floc formation index had better correlation format formation index than floc size. The relationships between wet web permeability and mat air permeability showed the significant linear correlation ($R^2$=0.97~0.98) for HML PAM and PEI. Floc formation index gave more useful information than the retention measurement when the performance of retention aids is evaluated at the laboratory before applying at the paper mill.