• Steel and Composite Structures
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• 제2권1호
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• pp.21-34
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• 2002

A model of the process of local buckling in tubular steel structural elements is presented. It is assumed that this degrading phenomenon can be lumped at plastic hinges. The model is therefore based on the concept of plastic hinge combined with the methods of continuum damage mechanics. The state of this new kind of inelastic hinge is characterized by two internal variables: the plastic rotation and the damage. The model is valid if only one local buckling appears in the plastic hinge region; for instance, in the case of framed structures subjected to monotonic loadings. Based on this damage model, a new finite element that can describe the development of local buckling is proposed. The element is the assemblage of an elastic beamcolumn and two inelastic hinges at its ends. The stiffness matrix, that depends on the level of damage, the yielding function and the damage evolution law of the two hinges define the new finite element. In order to verify model and finite element, several small-scale frames were tested in laboratory under monotonic loading. A lateral load at the top of the frame was applied in a stroke-controlled mode until local buckling appears and develops in several locations of the frame and its ultimate capacity was reached. These tests were simulated with the new finite element and comparison between model and test is presented and discussed.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2387-2393
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• 2020

In this study, a gradient material for shielding neutrons and gamma rays was developed, which consists of epoxy resin, boron carbide (B₄C), lead (Pb) and a little graphene oxide. It aims light weight and compact, which will be applied on the transportable nuclear reactor. The material is made up of sixteen layers, and the thickness and components of each layer were designed by genetic algorithm (GA) combined with Monte Carlo N Particle Transport (MCNP). In the experiment, the viscosities of the epoxy at different temperatures were tested, and the settlement regularity of Pb particles and B₄C particles in the epoxy was simulated by matlab software. The material was manufactured at 25 ℃, the Pb C and O elements of which were also tested, and the result was compared with the outcome of the simulation. Finally, the material's shielding performance was simulated by MCNP and compared with the uniformity material's. The result shows that the shielding performance of gradient material is more effective than that of the uniformity material, and the difference is most noticeable when the materials are 30 cm thick.

• 대한전기학회논문지
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• 제39권3호
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• pp.232-239
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• 1990

A new algorithm is suggested to solve the optimal reactive power and voltage control (optimal VAR control) problem. The model minimizes the real power losses in the system. The constraints include the reactive power limits of the generators, limits on the bus voltages and the operating limits of control variables-the transformer tap positions generator terminal voltages and switchable reactive power sources. The method presented herein, using a newly developed Jacobian decomposition method, employs linearized sensitivity relationships of power systems to establish both the objective function for minimizing the system losses and the system performance sensitivities relating dependent and control variables. The algorithm consists of two modules, i.e. the Q-V module for reactive power-voltage control, and load flow module for computational error adjustments. In particular the acceleration factor technique is introduced to enhance the convergence property in Q-V module. The combined use of the afore-mentioned two modules ensures more effective and efficient solutions for optimal reactive power dispatch problems. Results of the application of the method to a sample system and other worst-case systems demonstrated that the algorithm suggested herein is compared favourably with conventional ones in terms of computation accuracy and convergence characteristics.

• 한국전자파학회논문지
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• 제12권7호
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• pp.1076-1085
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• 2001

본 논문에서는 균일한 유전체 내의 복잡한 3차원 구조체에 대한 효율적인 기생(Parasitic) 임피던스 성분 추출을 위하여 반복법의 일종인 GMRES(Generalized Minimal RESidual Method)와 결합된 고속 멀티폴(FMM : Fast Multipole Method) 알고리즘을 구현하였다. 이 알고리즘은 준정적 기반 고속 멀티폴 방법으로 다중 도체들 간의 임피던스를 계산하는데 있어 기존의 모멘트법(MoM: Method of Moment)이 가지고 있는 계산량과 시간의 문제를 극복하기 위한 고속화 기술이다. 본 논문에서는 기존 MoM과의 비교를 통해 FMM의 정확성과 효율성을 입증하였다. 또한 멀티폴 알고리즘을 이용하여 기존 MoM으로는 해석이 불가능한 FC-PGA (Flip Chip Pin Grid Array) 패키지 핀에서의 기생 임피던스 성분들을 추출함으로써 신호간의 간섭에 의한 EMI/EMC 문제의 발생 가능성을 확인하였다.

• 한국세라믹학회지
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• 제45권1호
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• pp.1-29
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• 2008

In last two decades, an impressive progress has been recorded in terms of developing new materials or refining existing material composition/microstructure in order to obtain better performance in biomedical applications. The success of such efforts clearly demands better understanding of various concepts, e.g. biocompatibility, host response, cell-biomaterial interaction. In this article, we review the fundamental understanding that is required with respect to biomaterials development, as well as various materials and their properties, which are relevant in applications, such as hard tissue replacement. A major emphasize has been placed to present various design aspects, in terms of materials processing, of ceramics and polymer based biocomposites, Among the bioceramic composites, the research results obtained with Hydroxyapatite (HAp)-based biomaterials with metallic (Ti) or ceramic (Mullite) reinforcements as well as $SiO_2-MgO-Al_2O_3-K_2O-B_2O_3-F$ glass ceramics and stabilized $ZrO_2$ based bioinert ceramics are summarized. The physical as well as tribological properties of Polyethylene (PE) based hybrid biocomposites are discussed to illustrate the concept on how can the physical/wear properties be enhanced along with biocompatibility due to combined addition of bioinert and bioactive ceramic to a bioinert polymeric matrix. The tribological and corrosion properties of some important orthopedic metallic alloys based on Ti or Co-Cr-Mo are also illustrated. At the close, the future perspective on orthopedic biomaterials development and some unresolved issues are presented.

• Transactions on Electrical and Electronic Materials
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• 제3권3호
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• pp.8-13
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• 2002

Controlled precipitation of quasi-binary semiconductor system is newly proposed as an effective and reliable technique for the formation of well-defined and crystallographically aligned semiconductor nanostructures. Using HgTe-PbTe quasi-binary semiconductor system, self-aligned HgTe nanocrystallites distributed three dimensionally within PbTe matrix were successfully formed by the simple three step heat treatment process routinely found in age hardening process of metallic alloys. Examination of the resulting nano precipitates using conventional transmission electron microscopy (CTEM) and high resolution TEM (HRTEM) reveals that the coherent HgTe precipitates form as thin discs along the (100) habit planes making a crystallographic relation of {100}$\_$HgTe///{100}$\_$PbTe/ and [100]$\_$HgTe///[100]$\_$PbTe/. It is also found that the precipitate undergoes a gradual thickening and a faceting under isothermal aging up to 500 hours without any noticeable coarsening. These results, combined with the extreme dimension of the precipitates (4-5 nm in length and sub-nanometer in thickness) and the simplicity of the formation process, leads to the conclusion that controlled precipitation is an effective method for preparing desirable quantum-dot nanostructures.

• 분석과학
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• 제10권1호
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• pp.9-17
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• 1997

nitrophenol류는 미국 환경청에서 주요 priority 오염물질로 규정하고 있다. 물 중에 존재하는 nitrophenol류의 혼합물을 분석하기 위해 역상 액체크로마토그래피법에 대기압 화학이온화법을 연결한 질량분석기를 이용하였다. 추가적으로, 선택이온 검색법과 cone 전압차분해법(cone voltage fragmentation)을 이용하여 nitrophenol류의 확인에 있어서 감도와 선택성을 높였다. nitrophenol의 분해 형태는 충돌유발분해법인 MS/MS 기법으로 얻어진 분해 형태와 비교하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.207.2-207.2
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• 2013

Oxide-based thin film transistors have been attempted as powerful candidates for driving circuits for active-matrix organic light-emitting diodes and transparent electronics. The oxide TFTs are based on the amorphous multi-component oxides involving zinc, indium, and/or tin elements as main cation sources. The current work employed RF sputtering in order to deposit zinc-tin oxide thin films applicable to transparent oxide thin film transistors. The deposited thin film was characterized and probed in terms of materials and devices. The physical/chemical characterizations were performed using X-ray diffraction, Atomic Force Microscopy, Spectroscopic Ellipsometry, and X-ray Photoelectron Spectroscopy. The thin film transistors were fabricated using a bottom-gated structure where thermally-grown silicon oxide layers were applied as gate-dielectric materials. The inherent properties of oxide thin films are combined with the corresponding device performances with the aim to fabricating the multi-component oxide thin films being optimized towards transparent electronics.

• 한국재료학회지
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• 제9권6호
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• pp.569-576
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• 1999

In this study, the effect of the microstructural evolution on the electrical of Cu-Ag microcomposite was investigated. The nature of interfaces between silver filaments and Cu matrix may have pronounced effects on the physical properties of Cu-Ag filamentary microcomposites, little is known about these interfaces. In heavily drawn Cu-Ag filamentary microcomposities, the microstructure is too fine and the interfacial area is too large to maintsin a stable internal dislocation structure because of closely spaced filaments. Rather, most dislocations are thought to be gradually absorbed at the interfaces as the draw ratio increases. The mechanical and electrical properties of Cu-Ag filamentary microcomposites wires were also examined and correlated with the microstructural change caused by thermomechanical treatments. The study on the electrical conductivity combined to resistivity in Cu-Ag filamentary microcomposites and the rapid increase of the electrical conductivity at high annealing temperatures is mainly caused by the dissolution and coarsening of silver filaments. The relatively low ratio of the resistivities is mainly caused by the dissolution and coarsening of silver filaments. The relatively low ratio of the resistivities at 295K($\rho$\ulcorner/$\rho$\ulcorner) in as-drawn Cu-Ag microcomposites can also be explained by the contribution of the interface scattering.

• Advances in materials Research
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• 제6권4호
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• pp.329-341
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• 2017

The challenge of replacing conventional plastics with biodegradable composite materials has attracted much attention in product design, particularly in the tensile-related areas of application. In this study, fibres extracted from oil palm empty fruit bunch (EFB) were treated and utilized in reinforcing polyester matrix by hand lay-up technique. The effect of fibre loading and combined influence of alkali and silane treatments on porosity and water absorption parameters, and its correlation with the tensile behaviour of composites was analyzed. The results showed that tensile strength decreased whilst modulus of elasticity, water absorption and porosity parameters increased with increasing fibre loading. The composites of treated oil palm EFB fibre exhibited improved values of 2.47 MPa to 3.78 MPa for tensile strength; 1.75 MPa to 2.04 MPa for modulus of elasticity; 3.43% to 1.68% for porosity and 3.51% to 3.12% for water absorption at respective 10 wt.% fibre loadings. A correlation between porosity and water absorption with tensile behavior of composites of oil palm EFB fibre and positive effect of fibre treatment was established, which clearly demonstrate a connection between processing and physical properties with tensile behavior of fibre composites. Accordingly, a further exploitation of economic significance of oil palm EFB fibres composites in areas of low-to-medium tensile strength application is inferred.