• 한국통신학회논문지
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• 제18권7호
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• pp.989-998
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• 1993

랜덤다원접속 방식인 알로아는 간헐적인 패켓 전송 환경에서 기존의 고정할당 기법보다는 높은 효율을 얻을 수 있다. 그러나 슬롯형 알로아에서는 패켓이 채널에 슬롯별로 할당되기 때된에 슬롯과의 동기화가 중요한 문제가 된다. 위성 통신에서 동기화가 이루어지지 못한 패켓은 인접슬롯의 패켓과 충돌하므로 이러한 문제점을 해결하기위해 슬롯 사이에 보호시간이 포함된다. 기존의 알로아 채널에서는 두개 또는 =1이상의 패켓이 한 슬롯에 동시에 도착될 때 충돌이 발생되고 충돌된 패켓은 모두 재전송 알고리듬에 따라 다시 전송된다. 그러나 무선 환경에서 사용자들은 각각 다른 거리에서 채널을 공유하기 때문에 신호 전력은 달라진다. 실제적으로 신호점유 현상이 존재해서 동시에 수신된 패켓들 중에서 전력이 가장 큰 패켓이 선택되어 모든 패켓이 재전송 될 필요가 없다. 한편 대역확산 다원접속 방식에서는 가장 빨리 도착한 패켓이 선택된다. 본 논문에서는 보호시간과 신호점유 현상을 동시에 고려하여 백로그 상태변화를 추적하는 마르코프 모델로부터 수식적으로 정확한 슬롯형 알로아의 전송효율을 유도한다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.91-97
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• 2000

Once a response spectrum is estimated for the site, if there is a need of generating realistic earthquakes time histories considering seismic sources and path effects, one alternative is to use statistical phase characteristics based on real earthquake records other than assuming arbitrary duration and envelope curves. In this study, statistics of group delay times derived from Japanese strong earthquake data were used for phase generation to fully capture the stochastic property of earthquakes. The result shows that simulated earthquake time histories can be generated according to earthquake magnitude and distances with target response spectrum.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.426-431
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• 2000

A decoupled thermo-piezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.46-49
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• 2000

A decoupled thermo-~lezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

• Structural Engineering and Mechanics
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• 제76권1호
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• pp.17-26
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• 2020

The objective of this paper is to study the deformation in transversely isotropic thermoelastic solid using new modified couple stress theory subjected to ramp-type thermal source and without energy dissipation. This theory contains three material length scale parameters which can determine the size effects. The couple stress constitutive relationships are introduced for transversely isotropic thermoelastic solid, in which the curvature (rotation gradient) tensor is asymmetric and the couple stress moment tensor is symmetric. Laplace and Fourier transform technique is applied to obtain the solutions of the governing equations. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of length scale parameters are depicted graphically on the resulted quantities. Numerical results show that the proposed model can capture the scale effects of microstructures.

• 수산경영론집
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• 제36권1호
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• pp.27-49
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• 2005

This paper represents a critical review of current the relationship between aquaculture and the environment, focusing on the development of marine aquaculture for conservation of resources and environment in Korea. Aquaculture has grown rapidly during the past few decades in Korea. This expansion was possibly because of the growing demand for aquatic products and the failure of the capture fishery to keep pace with the demand. Nevertheless, the aquaculture industry must counter criticisms about adverse environmental effects and lack of sustainability. The productivity of Korean aquaculture is decreasing by environmental pollution, is suffering difficulty because competitive power of the aquaculture industry is weak, external effects of aquiculture is giving negative effects to coastal fishery. Therefore, aquaculture must improve as environmentally sound aquaculture for fisheries sustainability, and intensive aquaculture of high density must convert by low input sustainable aquaculture. Finally, the aquaculture system of Korea has to change to aquaculture for conservation of non - renewable resources and environment, it may contribute to development of Korean fisheries.

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.135-147
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• 2020

A methodology for evaluation of mechanical and thermal effects of localized non-axisymmetric oxidation in zircaloy claddings on LWR fuel reliability is proposed. To this end, the basic capabilities of the FALCON fuel behaviour code are used. Examples of methodology application to adjustment of selected operational limits for modern BWR fuel rods, to capture effects of the excess local oxidation, are presented. Specifically, the limiting rod internal pressure for the onset of cladding lift-off is reduced, depending on initial excess oxidation spot sizes. Also, the power limits for Anticipated Operational Occurrences are adjusted, to preclude fuel melting and cladding failure due to PCMI and PCI-SCC in the affected fuel rods.

• Geomechanics and Engineering
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• 제11권1호
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• pp.95-116
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• 2016

A novel higher order shear-deformable beam model, which provides linear variation of transversal normal strain and quadratic variation of shearing strain, is proposed to describe the beam resting on foundation. Then, the traditional two-parameter Pasternak foundation model is modified to capture the effects of the axial deformation of beam. The Masing's friction law is incorporated to deal with nonlinear interaction between the foundation and the beam bottom, and the nonlinear properties of the beam material are also considered. To solve the mathematical problem, a displacement-based finite element is formulated, and the reliability of the proposed model is verified. Finally, numerical examples are presented to study the effects of the interfacial friction between the beam and foundation, and the mechanical behavior due to the tensionless characteristics of the foundation is also examined. Numerical results indicate that the effects of tensionless characteristics of foundation and the interfacial friction have significant influences on the mechanical behavior of the beam-foundation system.

• 한국전문물리치료학회지
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• 제25권2호
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• pp.71-77
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• 2018

Background: There are insufficient objective or quantitative evidence for the better intervention to improve proprioception particularly for the application of external load. There are conflicting opinions whether the external load is effective for proprioception improvement or not. Objects: The purpose of this study was to investigate effects of external load on proprioception of shoulder joint quantitatively using 3D motion capture system. Methods: Nine healthy adults joined for this study. They were asked to perform scapular plane abduction motion with attaching reflective markers on the trunk and upper limb. The 3D positions of finger marker, while they performed the same task with and without external load, were recorded and analyzed. Results: All participants showed decreased variable errors in the vertical direction when the external load was applied (p<.02). Even though other directions (y, z) and absolute errors increased, they did not have statistical significances. Conclusion: Based on this study results, the external load application would be effective for shoulder joint position sense improvement.

• International Journal of Ocean System Engineering
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• 제2권3호
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• pp.151-159
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• 2012

The characteristics of an impact load and pressure were experimentally investigated. Drop tests were carried out using a modified Wigley with CB = 0.56. The vertical force, pressures, and vertical accelerations were measured. A 6-component load cell was used to measure the forces, piezo-electric sensors were used to capture the impact pressure, and strain-gauge type accelerometers were used to measure the vertical accelerations. A 50-kHz sampling rate was applied to capture the peak values. The repeatability of the measured data was confirmed and the basic characteristics of the impact load and pressure such as the linearity to the falling height were observed for all of the measurements. A simple formula was derived to extract the physical impact load from the measured force based on a simple mass-sensor-mass diagram, which was validated by comparing impact forces with existing data using the mathematical model of Faltinsen and Chezhian (2005). The effects of the elasticity of the model and change in acceleration during the water entry were investigated. It is interesting to observe that the impact loads occurred and reached peak values at the same time duration after water entry for all drop heights.