• 대한수학회지
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• 제59권2호
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• pp.255-278
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• 2022

In this paper, first we introduce a new notion of generalized Killing structure Jacobi operator for a real hypersurface M in complex hyperbolic two-plane Grassmannians SU_2,m/S (U₂·U_m). Next we prove that there does not exist a Hopf real hypersurface in complex hyperbolic two-plane Grassmannians SU_2,m/S (U₂·U_m) with generalized Killing structure Jacobi operator.

• 대한의생명과학회지
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• 제12권2호
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• pp.119-125
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• 2006

In relation to the tissue engineering, the cellular responses to the morphology of the scaffold surface are interesting topics. Human ligament fibroblasts (HLFs) were cultured on the micrpatterned silicone substrates subjected to cyclic stretch to simulate ligament motion. Groove and ridge width of silicone substrates was 10/50, 20/50, 20/10, and 20/20 ${\mu}m$ (groove/ridge ${\mu}m$) with a depth of $3{\mu}m$. Strain was applied over two days for 4 hours per day with a frequency of 0.5 Hz with the magnitudes of 4 or 8%. The purpose of this study was to evaluate ligament fibroblast alignment and cellular responses in relation to the pattern of microgrooved surface and stretching magnitude. Ligament fibroblasts in the microgrooved surface were elongated and aligned parallel to the microgrooves under no stretch. Uniaxial cyclic stretch induced cellular activities and their orientation rise in cellular response and the cells showed alignment and elongation perpendicular to the direction of the stretch. Biochemical analyses showed that the best cellular response was found on the $20/50{\mu}m$ under 8% stretch. The surface morphology and mechanical stretching were found to contribute to increase of proliferation, collagen production.

• 한국정보과학회논문지:시스템및이론
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• 제27권5호
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• pp.450-463
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• 2000

배열 재분산은 분산 메모리 컴퓨팅 환경에서 응용 프로그램의 수행 속도를 빠르게 하기 위해 많이 사용되고 있다. 특히 GEN BLOCK간 재분산은 동적으로 부하가 변화하는 경우 최적화된 성능을 보이기 위해 필요하다. 배열 재분산에 관한 기존 연구들은 대부분 CYCLIC(N)등과 같은 정규 분산 패턴간 재분산에 대해서만 이루어져 왔다. 그러나 GEN BLOCK등과 같은 비정규 분산 패턴간 재분산에서 발생하는 메시지패싱들은 정규 분산 패턴간 재분산과는 다른 특정을 보이기 때문에 이에 대한 새로운 연구가 필요하다. 본 논문은 GEN BLOCK간 재분산에서 발생하는 메시지패싱들에 정규 분산 패턴간 재분산에서 발견되 는 규칙성은 없는 반면 공간 지역성 (spacial locality)이 존재함을 보이고, 이를 기반으로 최소 스텝 정리와 최소 크기 정리가 재분산의 성능을 향상시키는데 중요함을 증병하였으며, 기존의 리스트 스케줄링 방식에 재구성 단계(relocation phase)를 추가함으로써 최적 스케줄을 생성하는 알고리즘을 제시하였다. 마지막으로 제안한 알고리즘의 성능을 평가하기 위해 ， CRAY T3E와 IBM SP2에서 성능 평가를 수행 하였으며， 그 결과 분산 메모리 병렬 머신에서 최소 스텝 정리와 최소 크기 정리를 만족하는 스케줄이 GEN BLOCK간 재분산의 성능 향상에 중요함을 보였다.

• The Journal of Advanced Prosthodontics
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• 제7권4호
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• pp.323-328
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• 2015

PURPOSE. This in-vitro study was designed to evaluate retention forces, microleakage and plastic deformation of a prefabricated 2-implant bar attachment system (SFI-Bar, Cendres+$M{\acute{e}}taux$, Switzerland). MATERIALS AND METHODS. Two SFI implant-adapters were torqued with 35 Ncm into two implant analogues. Before the tube bars were finally sealed, the inner cavity of the tube bar was filled with liquid red dye to evaluate microleakage. As tube bar sealing agents three different materials were used (AGC Cem (AGC, resin based), Cervitec Plus (CP; varnish) and Gapseal (GS; silicone based). Four groups with eight specimens each were tested (GS, GS+AGC, AGC, CP). For cyclic loading, the attachment system was assembled parallel to the female counterparts in a chewing simulator. The mean retention forces of the initial and final ten cycles were statistically evaluated (ANOVA, ${\alpha}{\leq}.05$). RESULTS. All groups showed a significant loss of retention forces. Their means differed between 30-39 N initially and 22-28 N after 50,000 loading cycles. No significant statistical differences could be found between the groups at the beginning (P=.224), at the end (P=.257) or between the loss of retention forces (P=.288). Microleakage occurred initially only in some groups but after 10,000 loading cycles all groups exhibited microleakage. CONCLUSION. Long-term retention forces of the SFI-Bar remained above 20 N which can be considered clinically sufficient. The sealing agents in this study are not suitable to prevent microleakage.

• Earthquakes and Structures
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• 제8권3호
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• pp.485-509
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• 2015

This paper presents the experimental results obtained by applying frequency-domain structural health monitoring techniques to assess the damage suffered on a special type of damper called Web Plastifying Damper (WPD). The WPD is a hysteretic type energy dissipator recently developed for the passive control of structures subjected to earthquakes. It consists of several I-section steel segments connected in parallel. The energy is dissipated through plastic deformations of the web of the I-sections, which constitute the dissipative parts of the damper. WPDs were subjected to successive histories of dynamically-imposed cyclic deformations of increasing magnitude with the shaking table of the University of Granada. To assess the damage to the web of the I-section steel segments after each history of loading, a new damage index called Area Index of Damage (AID) was obtained from simple vibration tests. The vibration signals were acquired by means of piezoelectric sensors attached on the I-sections, and non-parametric statistical methods were applied to calculate AID in terms of changes in frequency response functions. The damage index AID was correlated with another energy-based damage index -ID- which past research has proven to accurately characterize the level of mechanical damage. The ID is rooted in the decomposition of the load-displacement curve experienced by the damper into the so-called skeleton and Bauschinger parts. ID predicts the level of damage and the proximity to failure of the damper accurately, but it requires costly instrumentation. The experiments reported in this paper demonstrate a good correlation between AID and ID in a realistic seismic loading scenario consisting of dynamically applied arbitrary cyclic loads. Based on this correlation, it is possible to estimate ID indirectly from the AID, which calls for much simpler and less expensive instrumentation.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2949-2957
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• 2020

Fatigue crack growth model has been developed for dissimilar metal weld joints of a piping component under cyclic loading, where in the crack is located at the center of the weld in the circumferential direction. The fracture parameter, Stress Intensity Factor (SIF) has been computed by using principle of superposition as K_H + K_M. K_H is evaluated by assuming that, the complete specimen is made of the material containing the notch location. In second stage, the stress field ahead of the crack tip, accounting for the strength mismatch, the applied load and geometry has been characterized to evaluate SIF (K_M). For each incremental crack depth, stress field ahead of the crack tip has been quantified by using J-integral (elastic), mismatch ratio, plastic interaction factor and stress parallel to the crack surface. The associated constants for evaluation of K_M have been computed by using the quantified stress field with respect to the distance from the crack tip. Net SIF (K_H + K_M) computed, has been used for the crack growth analysis and remaining life prediction by Paris crack growth model. To validate the model, SIF and remaining life has been predicted for a pipe made up of (i) SA312 Type 304LN austenitic stainless steel and SA508 Gr. 3 Cl. 1. Low alloy carbon steel (ii) welded SA312 Type 304LN austenitic stainless-steel pipe. From the studies, it is observed that the model could predict the remaining life of DMWJ piping components with a maximum difference of 15% compared to experimental observations.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2017년도 춘계공동학술대회
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• pp.17-17
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• 2017

In electric agricultural machine the gearhead is needed to convert the high speed low torque rotation motion generated by DC motor to lower speed high torque motion used by the vehicle. The gearhead consist of several spur gears works as reduction gears. Spur gear have straight tooth and are parallel to the axis of the wheel. Spur gears are the most easily visualized gears that transmit motion between two parallel shafts and easy to produce. The modeling and simulation of spur gears in DC motor gearhead is important to predict the actual motion behavior. A pair of spur gear tooth in action is generally subjected to two types of cyclic stress: contact stress and bending stress including bending fatigue. The stress may not attain their maximum values at the same point of contact fatigue. These types of failure can be minimized by analysis of the problem during the design stage and creating proper tooth surface profile with proper manufacturing methods. To improve its life expectation in this study modal and stress analysis of gearhead is simulated using ansys work bench software based on finite element method (FEM). The modal analysis was done to understand gearhead deformation behaviour when vibration occurs. FEM static stress analysis is also simulated on gearhead to simulate the gear teeth bending stress and contact stress behavior. This methodology serves as an approach for gearhead design evaluation, and the study of gear stress behavior in DC motor gearhead which is needed in the small workshop scale industries.

• 전자공학회논문지
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• 제50권2호
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• pp.104-113
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• 2013

60GHz 멀티-기가비트 WPAN 시스템을 위한 고속 QC-LDPC 복호기의 구조를 제안한다. 제안한 QC-LDPC 복호기 설계를 위하여 4 블록-병렬 계층 복호 기술과 fixed wire network 기술이 적용 되었다. 2단 파이프라이닝과 4 블록-병렬 계층 복호기술은 동작 주파수와 데이터 처리량을 개선시키는데에 큰 효과가 있다. 또한 본 제안한 복호기 구조에서 스위치 네트워크를 구현하여 위하여 fixed wire network로 간단하게 구현될 수 있으면 하드웨어 복잡도를 크게 감소시킬 수 있다. 제안한 672-비트, rate-1/2인 QC-LDPC 복호기 구조는 90-nm CMOS 표준 셀을 이용해 설계 및 합성하였다. 성능 분석 결과 제안한 QC-LDPC 복호기 구조는 794K 게이트를 가지며 클락 속도 290MHz 에서 작동한다. 12-iteration일 때 데이터 처리율은 3.9 Gbps 이며 60GHz WPAN 시스템에 적용되어 사용 될 수 있다.

• 한국정밀공학회지
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• 제24권11호
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• pp.52-58
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• 2007

A cutting device capable of generating various shapes of the cyclic elliptical trajectory of a cutting tool was proposed and micro v-grooving experiments were performed to investigate the characteristics of elliptical vibration cutting (EVC). The proposed cutting device is comprised of a pair of parallel piezoelectric actuators with which harmonic voltages of varying phase difference and magnitude are supplied, creating various shapes of the elliptical tool path. The attributes of the elliptical locus involving the direction of the axis of an ellipse, the rotational direction and amplitudes of a trajectory were fine-tuned for stable operation of the EVC. The EVC characteristics performed with brass and copper revealed reduction in the cutting resistance and suppression of burr formation, resulting in the enhancement of form accuracy of machined micro-features. While the effect of the EVC increases with the increase of excitation frequency and the amplitude, it is found that a change in the cutting force decreases as the amplitude of an elliptical locus increases.

• 한국산업융합학회 논문집
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• 제21권4호
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• pp.159-165
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• 2018

In electric agricultural machine a reduction gear is needed to convert the high speed rotation motion generated by DC motor to lower speed rotation motion used by the vehicle. The reduction gear consists of several spur gears. Spur gears are the most easily visualized gears that transmit motion between two parallel shafts and easy to produce. The modelling and simulation of spur gears in DC motor reduction gear is important to predict the actual motion behaviour. A pair of spur gear tooth in action is generally subjected to two types of cyclic stress: contact stress and bending stress. The stress may not attain their maximum values at the same point of contact fatigue. These types of failure can be minimized by analysis of the problem during the design stage and creating proper tooth surface profile with proper manufacturing methods. To improve its life expectation in this study modal and stress analysis of reduction gear is simulated using ANSYS workbench based on finite element method (FEM). The modal analysis was done to understand reduction gear deformation behaviour when vibration occurs. FEM static stress analysis is also simulated on reduction gear to simulate the gear teeth bending stress and contact stress behaviour.