• Journal of Communications and Networks
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• 제17권3호
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• pp.306-320
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• 2015

Due to an explosive growth in services running in different datacenters, there is need for service selection and routing to deliver user requests to the best service instance. In current solutions, it is generally the client that must first select a datacenter to forward the request to before an internal load-balancer of the selected datacenter can select the optimal instance. An optimal selection requires knowledge of both network and server characteristics, making clients less suitable to make this decision. Information-Centric Networking (ICN) research solved a similar selection problem for static data retrieval by integrating content delivery as a native network feature. We address the selection problem for services by extending the ICN-principles for services. In this paper we present Queue and Latency, a network-driven service selection algorithm which maps user demand to service instances, taking into account both network and server metrics. To reduce the size of service router forwarding tables, we present a statistical method to approximate an optimal load distribution with minimized router state required. Simulation results show that our statistical routing approach approximates the average system response time of source-based routing with minimized state in forwarding tables.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2013년도 임시총회 및 하계학술연구발표회
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• pp.18-18
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• 2013

A FeRh alloy is a well-known efficient magnetocaloric material and some experimental and theoretical studies of bulk FeRh have been reported already by several groups. In this study we report first-principles calculations on magnetic properties of different thickness FeRh thin films in order to investigate the possibility to enhance further the magnetocaloric efficiency. We used Vienna Ab-initio Simulation Package (VASP) code. We found that the FeRh thin films have quite different magnetic properties from the bulk when the thickness is thinner than 6-atomic-layers. While bulk FeRh has a G-type antiferromagnetic (AFM) state, thin films which are thinner than 6-atomic-layers have an A-type AFM state or a ferromagnetic(FM) state. We will discuss possibility of magnetic phase transitions of the FeRh thin films in the view point of a magnetocaloric effect. And we found 4-, 5-, 6-layers films with Fe surface and 7-layers film with Rh surface are FM and they have dozens eV magnetocrystalline anisotropy (MCA) energy. MCA energy leads to determine energy barrier when magnetic states are changed by external magnetic field.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권1호
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• pp.67-76
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• 2012

Due to the increasing amount of applications of power electronic ac-dc converters, it is necessary to design a single-stage converter that can reliably perform both buck and boost operations. Traditionally, this can be achieved by double-stage conversion (ac/dc-dc/dc) which ultimately leads to less efficiency and a more complex control system. This paper discusses two types of modern ac-dc converters. First, the novel impedance-source ac-dc converter, abbreviated as custom Z-source rectifier, is analyzed; and then, switched inductor (SL) Z-source ac-dc converter is proposed. This paper describes the Z-source rectifiers' operating principles, the concepts behind them, and their superiorities. Analysis and simulation results show that the proposed custom Z-source rectifier can step up and step down voltage; and the main advantage of the SL Z-source ac-dc converter is its high step-up capability. Low ripple of the output dc voltage is the other advantage of the proposed converters. Finally, the SL Z-source ac-dc converter is compared with the custom Z-source ac-dc converter.

• EDISON SW 활용 경진대회 논문집
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• 제2회(2013년)
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• pp.294-298
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• 2013

A FeRh alloy is a well-known efficient magnetocaloric material and some experimental and theoretical studies of bulk FeRh have been reported already by several groups. In this study we report first-principles calculations on magnetic properties of different thickness FeRh thin films in order to investigate the possibility to enhance further the magnetocaloric efficiency. We used two methods of a Vienna Ab-initio Simulation Package (VASP) code and SIESTA package. We found that the FeRh thin films have quite different magnetic properties from the bulk when the thickness is thinner than 6-atomic-layers. While bulk FeRh has a G-type antiferromagnetic(AFM) state, thin films which are thinner than 6-atomic-layers have an A-type AFM state or a ferromagnetic (FM) state. We will discuss possibility of magnetic phase transitions of the FeRh thin films in the view point of a magnetocaloric effect. And we found 4-, 5-, 6-layers films with Fe surface and 7-layers film with Rh surface are FM and they have relatively small magnetocrystalline anisotropy (MCA) energy about less than 70 meV. The small MCA energy leads to reduction of the strength of magnetic field in operating a magnetic refrigerator.

• 소성∙가공
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• 제32권4호
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• pp.191-198
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• 2023

We examined the martensitic transformation kinetics for metastable stainless steel during electrochemical polishing (EP) using different types of electrolytes. Martensite fraction measured with EBSD showed that the electrolyte with high relative permittivity exhibited comparably higher levels of martensitic transformation. The amount of charge build-up on the specimen surface during EP with different types of electrolytes was calculated using COMSOL multiphysics simulations to understand these phase transformation characteristics. The effect of charge build-up-induced stress was analyzed using previously published first-principles calculations. We discovered that the electrolyte with high relative permittivity accumulated a greater amount of charge build-up, resulting in a stronger driving force for stress-induced martensitic transformation.

• 한국전기전자재료학회논문지
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• 제35권6호
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• pp.556-561
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• 2022

밀도범함수이론(density functional theory, DFT)이 등장한 이래로, 이를 재료과학에 적용하여 에너지 재료 및 반도체와 같은 전자재료들의 연구개발에 활발하게 활용되고 있다. 하지만 DFT 계산 프로그램을 실행할 때 필요한 입력 파일 생성 시 여러 가지 소재들에 대해 동일한 계산 조건을 맞춰 주고 파라미터들을 알맞게 설정해 줘야 올바른 계산 결과 비교가 가능한데, 이런 부분들에 대해 진입 장벽이 높다는 어려움이 있다. 이에 본 논문에서는 Python Materials Genomics (pymatgen) 파이썬 패키지를 이용해 분자 및 결정구조를 다루고 널리 사용되는 DFT 계산 프로그램인 Vienna Ab initio Simulation Package (VASP) 및 Gaussian 입력 파일 생성에 대해 소개하고자 한다. 이를 통해 해당 프로그램에 대한 전문적인 지식이 많지 않더라도 보다 일관적인 계산 조건에서 결과들을 손쉽게 수행할 수 있게 되기를 기대한다.

• Interaction and multiscale mechanics
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• 제2권1호
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• pp.69-89
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• 2009

Reinforced and prestressed concrete (RC and PC) thin walls are crucial to the safety and serviceability of structures subjected to shear. The shear strengths of elements in walls depend strongly on the softening of concrete struts in the principal compression direction due to the principal tension in the perpendicular direction. The past three decades have seen a rapid development of knowledge in shear of reinforced concrete structures. Various rational models have been proposed that are based on the smeared-crack concept and can satisfy Navier's three principles of mechanics of materials (i.e., stress equilibrium, strain compatibility and constitutive laws). The Cyclic Softened Membrane Model (CSMM) is one such rational model developed at the University of Houston, which is being efficiently used to predict the behavior of RC/PC structures critical in shear. CSMM for RC has already been implemented into finite element framework of OpenSees (Fenves 2005) to come up with a finite element program called Simulation of Reinforced Concrete Structures (SRCS) (Zhong 2005, Mo et al. 2008). CSMM for PC is being currently implemented into SRCS to make the program applicable to reinforced as well as prestressed concrete. The generalized program is called Simulation of Concrete Structures (SCS). In this paper, the CSMM for RC/PC in material scale is first introduced. Basically, the constitutive relationships of the materials, including uniaxial constitutive relationship of concrete, uniaxial constitutive relationships of reinforcements embedded in concrete and constitutive relationship of concrete in shear, are determined by testing RC/PC full-scale panels in a Universal Panel Tester available at the University of Houston. The formulation in element scale is then derived, including equilibrium and compatibility equations, relationship between biaxial strains and uniaxial strains, material stiffness matrix and RC plane stress element. Finally the formulated results with RC/PC plane stress elements are implemented in structure scale into a finite element program based on the framework of OpenSees to predict the structural behavior of RC/PC thin-walled structures subjected to earthquake-type loading. The accuracy of the multiscale modeling technique is validated by comparing the simulated responses of RC shear walls subjected to reversed cyclic loading and shake table excitations with test data. The response of a post tensioned precast column under reversed cyclic loads has also been simulated to check the accuracy of SCS which is currently under development. This multiscale modeling technique greatly improves the simulation capability of RC thin-walled structures available to researchers and engineers.

• 한국도로학회논문집
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• 제16권6호
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• pp.169-179
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• 2014

PURPOSES : This study is to conduct the research on the design principle for the driver's safety and comfort in installing consecutive curves of superhighway. METHODS : Superhighway does not currently exist in domestic area. Thus, this study is conducted by collecting driving behavior usage of 30 people who are involved in the members of the virtual driving simulation. By identifying the distribution characteristics of each scenario in ANOVA & Tukey Test, the distribution are categorized into three groups. RESULTS : In the case of Group A in Section 3 (R2 entry part), lane departure exceeds the safety standard, which means to be risky condition. And then in the case of Group B and C, the lane departure values applying theoretical formula was evenly distributed compared to the proven values. CONCLUSIONS : Based on the result, the continuous curve design principles at superhighway should follow three standards as follow. First, an additional linear part needs to be inserted between two curves. Second, what if inserting the linear part is difficult, it would be better to insert a curve more than 2,000m. Third, R1/R2 ratio should not be over two. This design primarily aims to the safety of the operator. Such road alignment also meets the expectations of drivers, thus, it may help drivers to be compatible and amenable while driving continuous curve in superhighway.

• Current Applied Physics
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• 제18권11호
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• pp.1320-1326
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• 2018

High crystalline quality CrN thin films have been grown on $La_{0.67}Sr_{0.33}MnO_3$ (LSMO) templates by molecular beam epitaxy. The structure and magnetic properties of CrN/LSMO heterojunctions are investigated combining with the experiments and the first-principles simulation. The N?el temperature of the CrN/LSMO samples is found to be 281 K and the saturation magnetization of CrN/LSMO increases compared to that of LSMO templates. The magnetic property of CrN/LSMO heterostructures mainly comes from Cr atoms of (001) CrN and Mn atoms of (001) LSMO. The (001) LSMO induces and couples the spin of the CrN sublattice at CrN/LSMO interface.

• 한국초등과학교육학회지:초등과학교육
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• 제41권3호
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• pp.538-552
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• 2022

본 연구에서는 Algodoo 시뮬레이션을 활용한 예비교사의 탐구 활동을 분석하여 그 특징을 이해하고 이를 통해 초등 예비교사를 위한 광학교육에 대한 교육적 시사점을 얻고자 하였다. 연구에는 교육대학의 1학년 학생 79명이 참여하였다. 학생들의 활동은 표상재생산, 확인실험, 탐구실험으로 구분할 수 있었다. 표상재생산을 수행한 학생들은 잘 알려진 권위 있는 표상을 시뮬레이션으로 나타냈으며 주요 특징을 포착하여 표상하였다. 확인실험을 수행한 학생들은 이론적 배경 조사를 통해 이미 알고 있는 개념을 확인하기 위한 실험을 수행하였으며, 주로 단순 탐구를 수행하였다. 탐구실험을 수행한 학생들은 현재 자신이 알지 못하는 것들을 시뮬레이션을 사용해 탐구하였으며 일반물리 이상에서 다루는 광학 현상에 대한 탐구를 수행한 학생도 있었다. 이상의 결과를 바탕으로 본 연구에서는 Algodoo를 활용한 자유로운 탐구 활동에서 학습자는 다양한 수준의 탐구 활동을 수행한다는 것을 확인하였다. 또한, Algodoo를 활용한 다양한 수준의 탐구 활동 예를 제시하고 Algodoo를 활용한 탐구 활동의 장단점과 이를 개선할 방안을 논의하였다.