• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.916-923
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• 2005

In this study, to observe aging effect of undrained shear behavior for Nak-Dong River sand, undrained static and cyclic triaxial tests were performed with changing relative density ($D_r$), consolidation stress ratio($K_c$) and consolidation time. As a result of the test, the modulus of elasticity to all samples estimated within elastic zone by the micro strain of about 0.05% in case of static shear behavior increased with the lapse of consolidation time significantly, so aging effect was shown largely. Also strength of phase transformation point(S_{PT}$) and strength of critical stress ratio point($S_{CSR}$) increased with the lapse of consolidation time. Undrained cyclic shear strength($R_f$) obtained from the failure strain 5% increased in proportion to relative density($D_r$) and initial static shear stress($q_{st}$), $R_f$ of consolidated sample for 1,000 minutes increased about 10.6% compared to that for 10 minutes at the loose sand, and $R_f$ increased about 7.0% at the medium sand. In situ application range of $R_f$ to the magnitude of earthquake for Nak-Dong River sand was proposed by using a increasing rate of $R_f$ as being aging effect shown from this test result.

• Restorative Dentistry and Endodontics
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• v.31 no.1
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• pp.50-57
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• 2006

The purpose of this study was to investigate influence of each file step of $ProTaper^{(R)}$ system on canal transportation. Twenty simulated canals were prepared with either engine-driven $ProTaper^{(R)}$ or manual $ProTaper^{(R)}$, Group R-resin blocks were instrumented with rotary $ProTaper^{(R)}$ and group M-resin blocks were instrumented with manual $ProTaper^{(R)}$. Pre-operative resin blocks and post-operative resin blocks after each file step preparation were scanned. Original canal image and the image after using each file step were superimposed for calculation of centering ratio The image after using each file step alld image after using previous file step were superimposed for calculation of the amount of deviation. Measurements were taken horizontally at five different levels (1 2, 3, 4 and 5 mm) from the level of apical foramen. In rotary $ProTaper^{(R)}$ instrumentation group, centering ratio and the amount of deviation of each step at all levels were not significantly different (p>0.05). In manual $ProTaper^{(R)}$ instrumentation group, centering ratio and the amount of deviation of each step at all levels except of 1 mm were not significantly different (p>0.05). At the level of 1 mn, F2 file step had significantly large centering ratio and the amount of deviation (p<0.05). Under the condition of this study, F2 file step of manual ProTaper tended to transport the apical part of the canals than that of rotary $ProTaper^{(R)}$.

• Journal of the Korean Operations Research and Management Science Society
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• v.40 no.4
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• pp.19-33
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• 2015

Recently, interest in research and development (R&D) investment decisions have increased among Korean domestic enterprises. However, existing R&D investment studies only focused on government R&D investment policies while only a few studies investigated firm level R&D investment. Prior literatures also overlooked the feedback loop between R&D investment and firm performance. Therefore, this paper identifies a system dynamics model for R&D investment decision making in domestic electronics firms. The conceptual model is derived from R&D investment-related theories found in bodies of literature on company performance, enterprise activity, and market maturity. This study investigates the dynamic feedback between R&D activities and sales using the system dynamics model. In other words, the system dynamics model is used to explain the change in the closed feedback circulation structure in R&D investment activities including technology development, production process, and marketing that subsequently result in sales increase and re-investment into R&D from the generated revenues. There are two major results. First, a similar ratio of investment on technology development and production process derives the higher company sales. Second, regardless of market maturity, marketing investment ratio positively affects sales and R&D budget growth. This study provides a system dynamics model to find the optimal ratio for R&D investment and suggests managerial strategic implications on electronic firm R&D investment decision making under market maturity condition.

• Journal of Korea Technology Innovation Society
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• v.21 no.1
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• pp.420-453
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• 2018

In the growth of the government's investment in national R&D project and the abuse of research expense, an effective control and management mechanism is strongly demanded. However, an excessive regulation might hinder the R&D performance, which also endangers the underlying objective of R&D policy. Especially, an excessive regulation on the R&D expenditure may damage the SMEs (Small and Medium sized Enterprises) where securing an adequate level of R&D funding is vital. This study investigates the R&D funding and R&D performance of SMEs participating in the national R&D project by using fixed effect panel model. As a result, this paper reveals the effectiveness of 'Government R&D subsidy'. However, that of 'private R&D fund' is not supported strongly. Also, this paper empirically demonstrates the efficiency of both 'Government R&D subsidy' and 'Private R&D fund' as the R&D costs are spent discretionarily (as the degree of 'Indirect Cost Ratio' increases). Especially, the effectiveness of 'Private R&D fund' can be moderated by 'Indirect Cost Ratio'. On the basis of the conclusions, this paper draws an implication that can increase R&D performance of SMEs through the interactions of manifold administrative values (i.e. effectiveness, efficiency and responsibility).

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.353-360
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• 2005

When the weight if a concrete member makes problems, or when the cost of the concrete is relatively high, it may be economical to use a hollow concrete member. But a hollow R.C Pier may have poor ductility because of the brittle failure at the inner face of the hollow R.C Pier. This brittle failure results from the absence of the confinement at the inner face of the hollow R.C Pier. To avoid this brittle failure an internally confined hollow R.C Pier was developed. Test results show that the energy ductility ratio of a internally confined hollow R.C Pier have a superior energy ductility ratio to a general hollow R.C Pier.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.176-184
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• 2005

When the weight if a concrete member makes problems. or when the cost of the concrete is relatively high, it may be economical to use a hollow concrete member. But a hollow R.C Pier may have poor ductility because of the brittle failure at the inner face of the hollow R.C Pier. This brittle failure results from the absence of the confinement at the inner face of the hollow R.C Pier. To avoid this brittle failure an internally confined hollow R.C Pier was developed. Test results show that the energy ductility ratio of a internally confined hollow R.C Pier have a superior energy ductility ratio to a general hollow R.C Pier.

• Journal of Korean Association for Spatial Structures
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• v.11 no.1
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• pp.121-130
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• 2011

Space frame structures have the advantage of constructing a large space structures without column and it may be considered as a shell structure. Nevertheless, with the characteristics of thin and long term of spacing, the unstable problem of space structure could not be set up clearly, and there is a huge difference between theory and experiment. Therefore, in this work, the tangential stiffness matrix of space frame structures is studied to solve the instability problem, and the nonlinear incremental analysis of the structures considering rise-span ratio(${\mu}$) and the ratio of load($R_L$) is performed for searching unstable points. Basing on the results of the example, global buckling can be happened by low rise-span ratio(${\mu}$), nodal buckling can be occurred by high rise-span ratio(${\mu}$). And in case of multi node space structure applying the ratio of load($R_L$), the nodal buckling phenomenon occur at low the ratio of load($R_L$), the global buckling occur a1 high the ratio of load($R_L$). In case of the global buckling, the load of bifurcation is about from 50% to 70% of perfect one's snap-through load.

• Journal of environmental and Sanitary engineering
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• v.15 no.3
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• pp.15-23
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• 2000

This study's purpose is the investigating the created liquid post-acid fermentation of usability of denitrification as exterior carbon sources by loading capacity of Organic matters. The time of acid fermentation of food waste, the slower loading capacity of organic matter, the faster decomposition fate, but the density of generation $VFA_S$ was weak and, $SBOD_5$ : ST-N rate and $SBOD_5/SCOD_{Cr}$ rate was low. Between TS and VS, VS was decreased to 6th day rast, and then was decreased slowly. Two days after stating the experiments, $SCOD_{Cr}$, $SBOD_5$, STOC and $VFA_S$ was decreased or increased slowly, and then increased fast. And after showing the highest density, it was tended to decreased fast. About 5 days after, because about 5 days later $CH_4$ bacteria activity due to the accumulation of $VFA_S$ was limited, $CH_4$ density was weak. When highest density in the acquisition of VFA, $R_1$ was $10,120mg/{\ell}$, $R_2$ was $11,380mg/{\ell}$, $R_3$was $13,720mg/{\ell}$. So $R_3$ only cut was highest generation. At the time of $SBOD_5$ with the highest density, at $SBOD_5$ : ST-N ratio, $R_1$ was 243:1, $R_2$ was 278:1, $R_3$ was 293:1. All of these were high $SBOD_5$ : ST-N ratios. And $R_3$ was the highest. After studying $SBOD_5$ : ST-N ratio and $SBCD_5/SCOD_{Cr}$ ratio, as a carbon source of biological denitrification it was profitable composition ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.275-281
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• 2016

In this study, we investigate the pool boiling enhancement caused by perforated plates on top of a smooth surface. We conduct tests using R-123 at atmospheric pressure. It was shown that perforated plates significantly enhanced the pool boiling of the smooth surface. The reason may be attributed to the increased bubble contact area between the plates. The results showed that the enhancement ratio was dependent on the heat flux. At high heat flux, the enhancement ratio increased as the porosity increased. However, at low heat flux, the enhancement ratio decreased as the porosity increased. For the present investigation, the optimum configuration had a pore diameter of 2.0 mm, pore pitch of $2.5mm{\times}5.0mm$ or $5.0mm{\times}5.0mm$, and a gap width of 0.5 mm, which yielded heat-transfer coefficients that are close to those of GEWA-T. The optimum porosity for R-123 was significantly larger than that of water or ethanol. The reason for this may be the large liquid-to-vapor density ratio along with the small latent heat of vaporization of R-123. The perforated plates yielded smaller boiling hysteresis compared with that of the smooth surface.

• Journal of the Korean Society of Physical Medicine
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• v.10 no.1
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• pp.37-43
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• 2015

PURPOSE: The purpose of this study is to investigate the effect of the physical therapy treatment room environment using microwave diathermy on the autonomic nervous system of human body. METHODS: Participants were 24 healthy adults. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences(RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were compared in microwave irradiation and non-irradiation group. Data were analyzed in Wilcoxon's signed-ranks test and Mann-Whitney U test. RESULTS: Standard deviation of all normal R-R intervals (SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different in microwave irradiation group. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different in microwave non-irradiation group. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different between two groups. CONCLUSION: There was no significant change in the sympathetic nervous system and parasympathetic nervous system regardless of the presence of microwave irradiation. There was no significant change in the autonomic nervous system adaptability regardless of the presence of microwave irradiation.According to this study, microwave diathermy does not have significant effect on the autonomic nervous system.Future study is necessary to investigate the long term effect of the physical therapy treatment room environment using microwave diathermy on the autonomic nervous system of the human body.