• Proceedings of the KWS Conference
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• 2010.05a
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• pp.93-93
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• 2010

환경 규제 및 배출가스 규제에 의하여 차량 경량화를 위해 점차적으로 Al합금의 차체 및 부품적용 비율이 점차 확대되고 있다. 이에 따라 알루미늄의 레이저 용접 시 출력, 초점거리, 용접 속도 등 공정 변수의 상관관계와 용접 결함 현상에 의한 관심이 집중된 연구가 많이 발표되었으며, 알루미늄 5000계열의 경우 박판 용접 시 기공, 균열 등 과 같은 결함 현상을 방지하기 위하여, Twin spot laser, Laser-TIG hybrid 등과 같은 공법 적용을 제안되었다. 본 연구에서는 Yb:YAG laser welding 시 Mg 함량이 높은 AA5J32을 소재를 이용하여 박판 겹치기 용접 시 Back side spiking 결함 방지를 위한 레이저 빔 출력 파형을 설계하여 실험을 수행하였다. 또한 파형의 특성에 따라 나타나는 겹치기 용접부의 기계적 특성과 기공에 대해 알아 보고자 하였다.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.42-42
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• 2010

알루미늄 합금은 질량 대비 강도가 우수하고 내식성 및 저온 특성이 양호하여 구조재로서 널리 사용되고 있다. 또한 그 사용 추세가 점점 증가 하고 있으며 알루미늄 합금의 용접을 위해 현재까지 다양한 용접 공정이 적용되었다. 일반적으로 GMAW, GTAW 등의 아크 용접과 박판의 경우 저항 점용접, 그 외의 $CO_2$ laser, Nd:YAG laser와 같은 고밀도 에너지 용접 공정에 의한 연구 결과들이 많이 발표 되었다. 하지만 알루미늄 합금의 특성 상 용접부에 기공과 균열과 같은 결함들이 각 공정에서 많이 발생하며 이러한 결함을 감소시키기 위한 용접기술에 관해 많은 연구가 진행되고 있다. 본 연구에서는 GMAW, Plasma-GMAW 공정을 적용하여 알루미늄 합금의 용접특성을 비교하였다. 알루미늄 합금 Al 5052, Al 6061 4mm 두께 모재에 대해 BOP(Bead On Plate) 용접실험을 실시하였으며 생산성 측면에서 각 공정에 따라 완전 용입 시 최대 용접 속도를 측정하여 비교하였다. 용접 품질 측면에서는 비드 표면 및 단면을 검사하고 인장시험을 수행하였으며, 용접 기공과 균열을 X-ray 촬영을 통해 비교하였다. 또한 고속카메라 촬영을 통해 용접 중 플라즈마로 인한 산화막 제거 효과를 확인하고 각 공정별 용접 시작부의 아크 안정성을 평가하였다. 인장시험 결과 모든 모드에서 모재에서 파단됨을 확인 하였고, Plasma-GMAW 공정의 경우 플라즈마의 예열효과로 인하여 GMAW 보다 완전용입 기준 용접속도가 빨랐으며, 청정작용도 우수한 것으로 확인되었다.

• IEMEK Journal of Embedded Systems and Applications
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• v.11 no.2
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• pp.87-95
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• 2016

Nonvolatile memory (NVM) is being considered as an alternative of traditional memory devices such as SRAM and DRAM, which suffer from various limitations due to the technology scaling of modern integrated circuits. Although NVMs have advantages including nonvolatility, low leakage current, and high density, their inferior write performance in terms of energy and endurance becomes a major challenge to the successful design of NVM-based memory systems. In order to overcome the aforementioned drawback of the NVM, extensive research is required to develop energy- and endurance-aware optimization techniques for NVM-based memory systems. However, researchers have experienced difficulty in finding a suitable simulation tool to prototype and evaluate new NVM optimization schemes because existing simulation tools do not consider the feature of NVM devices. In this article, we introduce a NVM-based cache simulator to support rapid prototyping and evaluation of NVM-based caches, as well as energy- and endurance-aware NVM cache optimization schemes. We demonstrate that the proposed NVM cache simulator can easily prototype PRAM cache and PRAM+STT-RAM hybrid cache as well as evaluate various write traffic reduction schemes and wear leveling schemes.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.783-790
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• 2012

Electric Vehicles(EVs) and Plug-in Hybrid Electric Vehicles(PHEVs) which have the grid connection capability, represent an important power system issue of charging demands. Analyzing impacts EVs charging demands of the power system such as increased peak demands, developed by means of modeling a stochastic distribution of charging and a demand dispatch calculation. Optimization processes proposed to determine optimal demand distribution portions so that charging costs and demand can possibly be managed. In order to solve the problems due to increasing charging demand at the peak time, alternative electricity rate such as Time-of-Use(TOU) rate has been in effect since last year. The TOU rate would in practice change the tendencies of charging time at the peak time. Nevertheless, since it focus only minimizing costs of charging from owners of the EVs, loads would be concentrated at times which have a lowest charging rate and would form a new peak load. The purpose of this paper is that to suggest a scenario of load leveling for a power system operator side. In case study results, the vehicles as regular load with time constraints, battery charging patterns and changed daily demand in the charging areas are investigated and optimization results are analyzed regarding cost and operation aspects by determining optimal demand distribution portions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.3
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• pp.289-293
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• 2013

In the noncoherent methods for UWB-IR (ultra-wideband impulse radio), block coded modulation (BCM) is better than the transmitted reference (TR) systems in terms of the energy efficiency and data rate. However, even BCM suffers from the performance degradation in the presence of strong inter-frame interference and inter symbol interference. We propose the transmitted reference based on the BCM (TR-BCM) which is the hybrid system of TR and BCM. Performance evaluation shows that the performance of TR-BCM is better than that of BCM in the high SNR range.

• Journal of the Korean Society for information Management
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• v.25 no.4
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• pp.131-148
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• 2008

The purposes of the study are to design a key-frame extraction algorithm for constructing the virtual storyboard surrogates and to evaluate the efficiency of the proposed algorithm. To do this, first, the theoretical framework was built by conducting two tasks. One is to investigate the previous studies on relevance and image recognition and classification. Second is to conduct an experiment in order to identify their frames recognition pattern of 20 participants. As a result, the key-frame extraction algorithm was constructed. Then the efficiency of proposed algorithm(hybrid method) was evaluated by conducting an experiment using 42 participants. In the experiment, the proposed algorithm was compared to the random method where key-frames were extracted simply at an interval of few seconds(or minutes) in terms of accuracy in summarizing or indexing a video. Finally, ways to utilize the proposed algorithm in digital libraries and Internet environment were suggested.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.2
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• pp.255-262
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• 2008

In this study, seismic response control performance of decentralized response-dependent MR damper which generates the control force using only the response of damper-installed floor, was experimentally investigated through the tests of a full-scale structure installed with large MR dampers. The performance of the decentralized control algorithm was compared to those of the centralized ones such as Lyapunov, modulated homogeneous friction, and clipped-optimal control. Hybrid mass damper were controlled to induce seismic response of the full-scale structure under El Centro earthquake. Experimental results indicated that the proposed decentralized MR damper provided superior or equivalent performance to centralized one in spite of using damper-installed floor response for calculating input voltage to MR damper.

• Journal of the Korean Society for Library and Information Science
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• v.43 no.4
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• pp.193-215
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• 2009

A more sophisticated library collection policy is required due to the changing information environment. Both traditional resources and diversified networked information resources are increasing continuously. The National Library of Korea should construct a systematic collection development policy in order to fulfill its mission. The purpose of this study is to develop a basic framework that is intended to improve the coverage of national collection. Examining previous studies and the national collection development policies of major advanced countries, a model consisting of four sub-models has been proposed. It includes hybrid collection, cooperative linking collection, collection evaluation, and a collection policy statement. Details of the sub-models and strategies are described.

• Proceedings of the KAIS Fall Conference
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• 2008.11a
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• pp.379-381
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• 2008

본 논문에서는 도시의 소음문제와 기존 방음벽의 문제를 근본적으로 해결하기 위해서는 도시 생태계를 고려한 생태식생방음벽의 개발이 필요하며 이를 위해 시스템 및 소재개발, 설계 및 시공기술들을 개발이 필요하다. 방음벽의 소음의 저감을 위한 단순한 구조물차원을 벗어나 소음 저감 기능을 가지는 환경친화적인 녹화구조물로 개발될 필요가 있다. 이는 절대 녹지의 부족과 단절로 인해 파생되는 도시 생태적 문제를 적극적으로 해결할 수 있는 현실적인 대안이 될 수 있을 뿐만 아니라, 도시경관 및 운전자와 주민 정서의 순화에 크게 기여할 것으로 예상된다. 결론적으로, 도시생태환경에 악영향을 가져왔던 기존의 방음벽에 반해서, 도시 전체적으로 녹지의 확대와 더불어 경관의 향상, 생태계 복원 등 시너지 효과를 가져올 식생방음벽의 개발은 도시환경의 질적 개선을 위한 현실적인 대안으로 연구 개발이 필요하다고 판단된다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.3
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• pp.68-74
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• 1998

Performance and efficiency of deep seabed collector is a primary factor for feasibility of commercial deep ocean mining. The efficiency of manganese nodules collector depends on vehicle mobility relative to undulating seafloor and is attributed pickup head to keep altitude and elevation of it against seafloor. For this reason, motion control of pickup head relative to the changing deep-sea topography and other disturbances is of particular importance in design of pickup device. The concept of design axiom is applied to a pickup device of hybrid type in order to evaluate the concept design. Kinematic analysis conducted in absolute Cartesian coordinates gives position, velocity, and acceleration of the hydraulic cylinders which enable the pickup head to keep the preset optimal distance from seafloor. Inverse dynamic analysis provides the driving forces of hydraulic cylinders and the reaction forces at each joint. Design sensitivity analysis is performed in order to investigate the effects of possible design variables on the change of the maximum strokes of hydraulic cylinders. The direct differentiation method is used to obtain the design sensitivity coefficients.