• Journal of the Korean Magnetics Society
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• v.22 no.4
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• pp.117-120
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• 2012

Compounds such as NaN belong to an interesting class of materials in which a magnetic order may appear despite the lack of d electrons. The magnetic properties of these materials are ascribed to the partially filled p shells. Recently, on the basis of electronic structure calculations from first principles, it has been found that NaN is a ferromagnetic half-metal in rocksalt (RS) and zinc-blende (ZB) structures with half-metallic band gaps in majority electron channels. The former structure has appeared to be more stable. From the first-principles calculation, we found that the half-metallic properties of the bulk RS and ZB NaN are conserved at the RS(001) and ZB(110) surfaces. Due to the interactions between Na s and N p electrons, N atoms become positively polarized. In the RS NaN (001) the calculated values of the magnetic moments of the N atoms is about $0.73{\mu}_B$. The magnetic moment on the N atom in the top most layer of ZB(110) is slightly larger than that of the RS(001) surface, i.e., $0.75{\mu}_B$. The Na atoms in the both structure are hardly polarized.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.49-54
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• 2005

Inner Structured and Bonded(ISB) panel, a kind of metallic sandwich panel, consists of two thin skin plates bonded to a micro-patterned inner structure. Its overall thickness is $1\~3mm$and it has attractive properties such as ultra-lightweight, high efficiency in stiffness-to-weight and strength-to-weight ratio. In many previous studies, resistance welding, brazing and adhesive bonding are studied for joining the panel. However these methods did not consider productivity, but focused on structural characteristics of joined panels, so that the joining process is very complicated and expensive. In this paper, a new joining process with resistance welding is developed. Curved surface electrodes are used to consider the productivity and the stopper is used between electrodes during welding time to maintain the shape of inner structure. Welding time, gap of electrodes and distance between welding points are selected as the process parameters. By measuring the tensile load with respect to the variation of welding time and gap of electrodes, proper welding conditions are studied. Welding time is proper between 1.5-2.5cycle. If welding time is too long, then inner structures are damaged by overheating. Gap of electrode should be shorter than threshold value fur joint strength, when total thickness of inner structure and skin plate is 3.3mm, the threshold distance is 3.0mm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1050-1053
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• 2002

This paper presents metal structure that is fabricated using UV-LIGA process with PMER N-CA3000. In order to fabricate metal structure with high aspect ratio, the systematic optimization method was adopted and then the structure of $36{\mu}m$ thick mold with aspect ratio 7:1 (trench) and $32{\mu}m$ thick nickel structure was obtained. This structure is applied to the fabrication of optical switch.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.344.1-344.1
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• 2016

Recently, graphene has shown great characteristic of electrical conductivity, strength, and elasticity. However, due to edge unstable and metallic properties, it is difficult to use as a semiconductor devices. The solution of such problems has been sought a way to use the boron nitride in a stacked layer structure. By graphene and boron nitride stacked layer structure on silicon substrate, the electron mobility is improved and deteriorated results in semiconductor properties. In this study, to make layered structure, we developed direct synthesis method for graphene on boron nitride. By using Raman technique, the directly stacked layer structure is in good agreement with measurements on each of the attributes.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.380-383
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• 2003

In this paper, we analyzed the characteristics of a modified DGS(Defected Ground Ground Structure)and extracted the equivalent citcuit of that. The proposed DGS is the structure that connects two DGS units, which are composed of the defects on the metallic ground plane and the gab on the signal line. The gab on the signal line was adopted to induce series capacitor of band pass filter. Also, to confirm the validity of the proposed structure, we designed and implemented C - Band pass filter by using the modified DGS.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.42-45
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• 2009

We report simple structure red phosphorescent devices comprising only single organic layer structure. Maximum current efficiency of 9.44 cd/A and the driving voltage of 5.4 V are obtained in this single layer structure PHOLEDs, respectively. The mixed host system using electron transporting and hole transporting materials doped with $Ir(piq)_3$ provides such high efficiency and reasonable driving voltage. The principal to simplification is the direct charges injection from the metallic electrodes into mixed host materials.

• Journal of Magnetics
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• v.20 no.1
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• pp.1-7
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• 2015

We investigated the half-metallicity and magnetism at the (001) and (110) surfaces of YC in zinc-blende structure by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. From the calculated local density of states, we found that neither (001) nor (110) surface preserves the half-metallicity. While the magnetic moment of Y atom in the YC bulk is $0.116{\mu}_B$, it is $0.057{\mu}_B$ at the topmost layer of Y-terminated (001) surface. On the contrary, C-terminated (001) YC surface exhibits stronger magnetism than the bulk structure; the calculated magnetic moment on topmost C atom is $1.084{\mu}_B$, while that of C atom in the bulk structure is $0.423{\mu}_B$. The magnetic properties of the non-polar (110) YC surface are slightly enhanced as compared with the bulk structure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.346-351
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• 2018

Metal three-dimensional (3D) printing technologies are mainly classified as powder bed fusion (PBF) and direct energy deposition (DED) methods according to the method of application of a laser beam to metallic powder. The DED method can be used to fabricate fine and hard 3D metallic structures by applying a strong laser beam to a thin layer of metallic powder. The PBF method involves slicing 3D graphics to be a certain height, laminating metal powders, and making a 3D structure using a laser. While the DED method has advantages such as laser cladding and metallic welding, it causes problems with low density when 3D shapes are created. The PBF method was introduced to address the structural density issues in the DED method and makes it easier to produce relatively dense 3D structures. In this paper, thin lines were produced by using PBF 3D printers with stainless-steel powder of roughly $30{\mu}m$ in diameter with a galvano scanner and fiber-transferred Nd:YAG laser beam. Experiments were carried out to find the optimal conditions for the width of a line depending on the processing times, laser power, spot size, and scan speed. The optimal conditions were two scanning processes in one line structure with a laser power of 30 W, spot size of $28.7{\mu}m$, and scan speed of 200 mm/s. With these conditions, a minimum width of about $85.3{\mu}m$ was obtained.

• Journal of the Korean Magnetics Society
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• v.26 no.6
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• pp.185-189
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• 2016

By employing photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS), the electronic structure of the candidate half-metallic antiferromagnet of $Mn_3Ga$ Heusler compound has been investigated. We have studied two ball-milled $Mn_3Ga$ powder samples, one after annealing and the other without annealing, respectively. Based on the Mn 2p XAS study, we have found that Mn ions are nearly divalent in $Mn_3Ga$ and that the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry are both present in $Mn_3Ga$. We have found relatively good agreement between the measured valence-band PES spectrum of $Mn_3Ga$ and the calculated density of states, which is in agreement with the half-metallic electronic structure of $Mn_3Ga$.

• Earthquakes and Structures
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• v.14 no.1
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• pp.1-10
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• 2018

Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.