• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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• pp.308-315
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• 2019

In this study, numerical simulations of slamming impact pressure acting on the flat plate and wedge type models using the cartesian-grid system and Modified Marker-Density Method (MMD method) were performed and the results were examined. The flat plate and wedge type models were selected as target objects, the turbulence characteristics were considered by applying the Sub-Grid Scale (SGS) turbulence model. Through this study, how the pressure acting on the target objects according to the incident angle influences the slamming impact pressure was examined and the results were compared with the flow characteristics of other experimental results. Also, the degree of slamming impact pressure is evaluated with respect to the cartesian-grid system and MMD method, which is easy to use and has a high degree of calculation for free surface.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.2
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• pp.6-12
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• 1998

Thin film SOI(Silicon-on-insulator) device offer unique advantages such as reduction in short channel effects, improvement of subthreshold slope, higher mobility, latch-up free nature, and so on. But these devices exhibit floating-body effet such as current kink which inhibits the proper device operation. In this paper, the SOI NMOSFET with a T-type gate structure is proposed to solve the above problem. To simulate the proposed device with TSUPREM-4, the part of gate oxide was considered to be 30nm thicker than the normal gate oxide. The I-V characteristics were simulated with 2D MEDICI. Since part of gate oxide has different oxide thickness, the gate electric field strength is not same throughout the gate and hence the impact ionization current is reduced. The current kink effect will be reduced as the impact ionization current drop. The reduction of current kink effect for the proposed device structure were shown using MEDICI by the simulation of impact ionization current, I-V characteristics, and hole current distribution.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.19 no.1
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• pp.51-56
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• 2013

From the time the product is manufactured until it is carried and ultimately used, the product is subjected to some form of handling and transportations. During this process, the product can be subjected to many potential hazards. One of them is the damage caused by shocks. In order to design a product-package system to protect the product, the peak acceleration or G force to the product that causes damage needs to be determined. When a corrugated fiberboard box loaded with products is dropped onto the ground, part of the energy acquired due to the action of the gravitational acceleration during the free fall is dissipated in the product and the package in various ways. The shock absorbing characteristics of the packaging cushion materials are presented as a family of cushion curves in which curves showing peak accelerations during impacts for a range of static loads are shown for several drop heights. The new method for determining the shock absorbing characteristics of cushioning materials for protective packaging has been described and demonstrated. It has been shown that cushion curves can be produced by combining the static compression and impact characteristics of the material. The dynamic factor was determined by the iterative least mean squares (ILMS) optimization technique in which the discrepancies between peak acceleration data predicted from the theoretical model and obtained from the impact tests are minimized. The approach enabled an efficient determination of cushion curves from a small number of experimental impact data.

• Journal of Korea Trade
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• v.25 no.3
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• pp.48-64
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• 2021

Purpose - This study examined the effect of tariff cuts on productivity in Korea's manufacturing industries and the effect of initial productivity level before tariff cuts on productivity improvement after tariff cuts. We also attempted to identify whether import-driven or export-driven factors are more important for productivity improvement, especially in low productivity industries. Design/methodology - Since tariff reduction is a policy decision that can affect cross-industry, its impact is spread across all industries beyond the scope of a single firm through the input and output network of industry structure. Accordingly, we proposed a new method to measure the change in productivity to reflect the impact of tariff cuts across industries. Through an Armington CGE analysis, changes in endogenous variables can be directly measured after the exogenous shock of tariff reduction, and the amount of movements in productivity triggered by tariff cuts can also be calculated. We can thus assess the effectiveness of exogenous policy, such as tariff cuts, through the difference between the benchmark and counterfactual values of endogenous variables. Findings - This study confirmed that tariff reduction positively affected productivity improvement in Korea's manufacturing industries. It also confirmed that productivity gains occur in Korea's leading export industries. Finally, greater productivity gains were recorded in the group with additional high-export-share or high-import-share conditions for low productivity industries. These results are, in a limited sense, consistent with the existing studies that emphasize the importance of exports and imports on productivity improvement, especially for low productivity industries. Originality/value - The results of our experiments are different from those of non-CGE studies, which measure the industry-level change in productivity with dummy coefficients, in terms of directly calculating the amount of change in productivity. In addition, we propose that the Armington CGE model is more appropriate than the Melitz CGE model to directly measure the productivity after tariff cuts. This is because the Melitz CGE model assumes the given specific productivity density, which does not change after an overall drop of tariffs. To the best of our knowledge, this approach to directly calculating productivity by reflecting the impact of tariff reduction across industries through CGE analysis, is unprecedented in this literature.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1358-1363
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• 2003

Due to the application of Integrated Head Assembly (IHA) in KSNP+ reactor design, an investigation of reactor internals integrity is carried out to assure that the adoption of IHA does not affect the safety of reactor operation. One of the postulated accident events is the R.V. closure head fall from 5.5m high directly above the reactor vessel that may occur during the refueling operation. The analysis model consists of lumped mass elements of the entire reactor vessel and internals. Because of extreme load, separate elastic-plastic analyses are done for the members that undergo plastic deformation. The analysis verified that the stresses of the reactor internals and the fuel assemblies are within the bound of allowable stress limits and the integrity of the fuel assemblies is maintained.

• Journal of Biomedical Engineering Research
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• v.20 no.2
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• pp.231-236
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• 1999

Understanding the exgenous water induced thermomechanical effect on the dental hard tissue by the Q-switched Er:YAG laser (1-$mutextrm{s}$-long pulse width) has an important impact on the further understanding of the free-running Er:YAG laser (250-$mutextrm{s}$-long pulse width) ablation on the dental gard tissue because one macroscopic effect in the free-running laser is an accumulation of microscopic effects we investigated in this study. The Q-switched Er:YAG laser with exogenous water on the tooth enhanced ablation rate compared to the case of no water on the tooth. The frequency of exogenous-water jet on the tooth has affected the ablation rate in such a way that as we dispensed water drops less frequently we could get more enhanced ablation rate. The amplitude of the recoil pressure depends on the tooth surface conditions such that as surfaces wet, and as the volume of the exogenous water drop increased, the amplitude of the recoil pressure increased also. From this study we realized that the 1 $mutextrm{s}$ long pulsed induced thermomechanical effect provides us useful information for the understanding of the free-running Er:YAG laser induced ablation with exogenous water.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2133-2138
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• 2003

In general, flow entrainment of surrounding gas into a supersonic jet is caused by the pressure drop inside the jet and the shear actions between the jet and the surrounding gas. In the recent industrial applications, like supersonic ejector system or scramjet engine, the rapid mixing of two different gases is important in that it determines the whole performance of the flow system. However, the mixing performance of the conventional circular jet is very low because the shear actions are not enough. The supersonic jet discharging from a petal nozzle is known to enhance mixing effects with the surrounding gas because it produces strong longitudinal vortices due to the velocity differences from both the major and minor axes of petal nozzle. This study aims to enhance the mixing performance of the jet with surrounding gas by using the lobed petal nozzle. The jet flows from the petal nozzle are compared with those from the conventional circular nozzle. The petal nozzles employed are 4, 6, and 8 lobed shapes with a design Mach number of 1.7 each, and the circular nozzle has the same design Mach number. The pitot impact pressures are measured in detail to specify the jet flows. For flow visualization, the schlieren optical method is used. The experimental results reveal that the petal nozzle reduces the supersonic length of the supersonic jet, and leads to the improved mixing performance compared with the conventional circular jet.

• Journal of Periodontal and Implant Science
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• v.42 no.6
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• pp.217-223
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• 2012

Purpose: Several parameters have been described for determining the success or failure of dental implants. The surface properties of transgingival implant components have had a great impact on the long-term success of dental implants. The purpose of this study was to compare the tendency of two periodontal pathogens to adhere to and colonize zirconia abutments and titanium alloys both in hard surfaces and soft tissues. Methods: Twelve patients participated in this study. Three months after implant placement, the abutments were connected. Five weeks following the abutment connections, the abutments were removed, probing depth measurements were recorded, and gingival biopsies were performed. The abutments and gingival biopsies taken from the buccal gingiva were analyzed using real-time polymerase chain reaction to compare the DNA copy numbers of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and total bacteria. The surface free energy of the abutments was calculated using the sessile water drop method before replacement. Data analyses used the Mann Whitney U-test, and P-values below 0.05 find statistical significance. Results: The present study showed no statistically significant differences between the DNA copy numbers of A. actinomycetemcomitans, P. gingivalis, and total bacteria for both the titanium and zirconia abutments and the biopsies taken from their buccal gingiva. The differences between the free surface energy of the abutments had no influence on the microbiological findings. Conclusions: Zirconia surfaces have comparable properties to titanium alloy surfaces and may be suitable and safe materials for the long-term success of dental implants.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.18-31
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• 2018

Rotorcrafts have more severe crashworthiness conditions than fixed wing aircraft owing to VTOL and hovering. Recently, with the increasing demand for highly efficient transportation system, application of composite materials to aircraft structures is increasing. However, due to the characteristics of composite materials that are susceptible to impact and crash, demand to prove the crashworthiness of composite structures is also increasing. The purpose of present study is to derive the structural concept of composite subfloor for rotorcrafts and verify it. In order to design a crashworthy composite subfloor, the conceptual design of the testbed helicopter for the demonstration and the derivation of energy absorbing requirement were carried out, and the composite energy absorber was designed and verified. Finally, the testbed for the demonstration of a crashworthy composite structure was fabricated, and performed free drop test. It was confirmed that the test results meet the criteria for ensuring occupant survivability.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.35.2-35.2
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• 2009

최근 본 연구실에서 무연 솔더를 위한 새로운 Cu-Zn 합금 젖음층을 개발하였다. 전해도금을 통하여 Cu-Zn 합금층을 형성한 뒤 그 위에 Sn-4.0wt% Ag-0.5wt% Cu (SAC 405) 솔더를 리플로 솔더링을 통해 솔더접합부를 형성하였으며 계면에서 생성된 금속간 화합물의 형성 및 성장 거동을 연구하였다. SAC/Cu 시스템의 경우, $150^{\circ}C$에서 시효 처리를 실시하는 동안 솔더와 도금된 Cu 계면에서 $Cu_6Sn_5$ 상과 미세한 공공이 형성된 $Cu_3Sn$ 상이 발견되었다. 반면에 SAC/Cu-Zn 시스템에서는 계면에서 $Cu_6Sn_5$ 상만이 형성되었다. 또한 큰 판상형의 $Ag_3Sn$ 상이 SAC/Cu 시스템에 비해 현저하게 억제되었다. SAC/Cu-Zn 계면에서의 금속간 화합물의 성장 속도가 SAC/Cu 계면에서 형성된 금속간 화합물의 성장 속도보다 느리게 나타났다. Cu-Zn 젖음층의 Zn가 솔더와 Cu-Zn 층 사이에서 Cu와 Sn 원자의 상호 확산을 방해하기 때문이다. 본 연구에서는 Cu와 Cu-Zn 층을 이용한 솔더 접합부의 낙하 충격 신뢰성을 연구하였다. 낙하 충격 시험 시편은 두 개의 인쇄 회로 기판을 SAC 405 솔더볼을 이용하여 리플로를 통해 상호연결 하여 제조되었다. 이 때, 각각의 인쇄 회로 기판의 패드에는 Cu 층과 Cu-Zn층을 전해도금을 통하여 각각 $10{\mu}m$두께의 젖음층을 형성하였다. 낙하 시험 시편을 제조한 뒤, 시효 처리에 대한 낙하 저항 신뢰성의 특성을 연구하기 위해 250, 500 시간동안 시효처리를 한 후 각 조건에서 계면에 형성된 금속간 화합물의 성장 거동을 관찰하였으며, 낙하 충격 시험을 실시하였다. 낙하 시험은 daisy chain으로 연결된 시편의 저항이 100 Ohm 이상 측정되었을 때 중단되도록 하였다. Cu-Zn/SAC/Cu-Zn 시편의 경우 초기 리플로를 하였을 때 불량이 발생하는 평균 낙하 수는 350이며, Cu/SAC/Cu 시편의 평균 낙하수는 200 미만으로 나타났다. Cu/SAC/Cu 시편의 경우, 시효처리 시간이 증가함에 따라 평균 낙하수는 큰 폭으로 감소하였지만, Cu-Zn/SAC/Cu-Zn 시편은 불량이 발생하는 평균 낙하수의 감소폭이 보다 완만하게 나타났다. Cu 층에 Zn를 첨가함으로써 솔더와 젖음층 사이에서 형성된 금속간 화합물의 성장 및 미세 공공의 형성이 억제되었고, 솔더 접합부의 과냉을 감소시킴으로써 큰 판상형의 $Ag_3Sn$ 상의 형성을 억제함으로써 Cu-Zn/SAC/Cu-Zn 솔더 접합부에서 Cu/SAC/Cu 솔더 접합부보다 낙하 충격에 대한 저항성 및 신뢰성이 향상되었다. 이는 무연 솔더에 Zn를 첨가하여 낙하 충격 신뢰성을 향상시킨 것과 동일한 효과를 나타냈음을 확인하였다. 본 연구는 한국 과학 기술 재단의 전자패키지 재료 연구 센터(CEPM)와 지식 경제부의 부품 소재 기술 개발 사업의 지원을 받아 수행되었습니다.