• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.454-457
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• 2019

Controlling the shape of Ag nanoparticles (NPs) is very difficult. In the present work, urchin Ag NPs with different sizes and pod length control have been synthesized successfully in high yield by the concentration of a reducing agent. Unique Ag NPs were observed by TEM and SEM. These nanocrystals exhibit tunable surface plasmon resonance properties from the visible to near-infrared regions. They were applied to surface-enhanced Raman scattering (SERS) substrates using rhodamine 6G (R6G), benzenethiol (BT), and 4-amino benznethiol (4-ABT) molecules. The enhanced local field effect due to the sharp pod length, size, and surface plasmon of the urchin Ag NPs resulted in enhanced SERS properties and can serve as high-sensitivity substrates for SERS measurements.

• Korean Journal of Materials Research
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• v.18 no.3
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• pp.148-152
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• 2008

A new cost-effective atomic layer deposition (ALD) technique, known as Proximity-Scan ALD (PS-ALD) was developed and its benefits were demonstrated by depositing $Al_2O_3$ and $HfO_2$ thin films using TMA and TEMAHf, respectively, as precursors. The system is consisted of two separate injectors for precursors and reactants that are placed near a heated substrate at a proximity of less than 1 cm. The bell-shaped injector chamber separated but close to the substrate forms a local chamber, maintaining higher pressure compared to the rest of chamber. Therefore, a system configuration with a rotating substrate gives the typical sequential deposition process of ALD under a continuous source flow without the need for gas switching. As the pressure required for the deposition is achieved in a small local volume, the need for an expensive metal organic (MO) source is reduced by a factor of approximately 100 concerning the volume ratio of local to total chambers. Under an optimized deposition condition, the deposition rates of $Al_2O_3$ and $HfO_2$ were $1.3\;{\AA}/cycle$ and $0.75\;{\AA}/cycle$, respectively, with dielectric constants of 9.4 and 23. A relatively short cycle time ($5{\sim}10\;sec$) due to the lack of the time-consuming "purging and pumping" process and the capability of multi-wafer processing of the proposed technology offer a very high through-put in addition to a lower cost.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.82-86
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• 1995

Using electrocardiography is a common method to diagnose heart disease, Modeling and simulation of activation process for the heart system is useful to understand electrocardiography. This paper proposes a two-dimensional cellular automata model for the activation process of the ventricles. The model represents the geometry of the ventricles by the ellipsoidal shape in two dimension. In the model, ventricles are divided into four layers, each of which has a set of cells with preassigned properties. The proposed model takes Into account the local orientation of the myocardial fibers and their distributed velocity, and refractory period. Simulation experiment is performed to measure activation potential for each cell in each layer within the ventricles.

• Journal of Magnetics
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• v.15 no.3
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• pp.108-111
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• 2010

Fe50Cr50 metastable alloys were prepared by the mechanical alloying method with milling periods of 1, 2, 4, 6, 12 and 24 hours, respectively. The structural evolution was analyzed by the extended x-ray absorption fine structure (EXAFS). In this work, the EXAFS analysis provided the local structural information around Fe central atom. The saturation magnetization was also measured by VSM. The magnetization decreased as the process mechanical alloying progressed. The magnetic property was related to the local structural variation as a function of processing time. The analysis showed that the diffusion Cr atoms into Fe clusters caused the reduction of magnetization. EXAFS analysis exhibited that the local ordering of magnetic atoms caused the magnetic ordering. Also, EXAFS analysis showed that the long range order of Fe atoms was destroyed completely in 24 hour milling.

• Journal of Magnetics
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• v.18 no.1
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• pp.1-4
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• 2013

Structural and magnetic properties of $Fe_{50}Mn_{50}$ nanocrystalline alloys prepared by the mechanical alloying technique (using commercial Fe and Mn powders as the precursors) are studied as a function of milling time, 1 hr to 48 hrs. The nano-crystallite size and shape are examined by using scanning electron microscopy (SEM). The effect of milling time on structural characterization was investigated using X-ray diffractometer (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). Both XRD and EXAFS studies showed that the alloying process should be completed after 36 hrs milling. Concerning the magnetic behavior, the data obtained from superconducting quantum interference devices (SQUID) exhibited both magnetic saturation ($M_s$) and coercivity ($H_c$) depend strongly on the milling time, which are related to the changes in the crystallite size and magnetic dilution.

• Journal of the Korean Magnetics Society
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• v.23 no.3
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• pp.110-116
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• 2013

This paper proposes a sampling-based sensitivity method for dealing with electromagnetic coupled design problems effectively. The black-box modeling technique is basically applied to obtain an optimum regardless of how strong the electromagnetic, thermal and structural analyses are coupled with each other. To achieve this, Kriging surrogate models are produced in a hyper-cubic local window with the center of a current design point. Then design sensitivity values are extracted from the differentiation of basis functions which consist of the models. The proposed method falls under a hybrid optimization method which takes advantages of the sampling-based and the sensitivity-based methods. Owing to the aforementioned feature, the method can be applied even to electromagnetic problems of which the material properties are strongly coupled with thermal or structural outputs. To examine the accuracy and validity of the proposed method, a strongly nonlinear mathematical example and a coil design problem for local induction heating are tested.

• 전기의세계
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• v.29 no.8
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• pp.511-518
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• 1980

The thermostimulated discharge currents of low-density polyethylene electrets were measured versus the principal experimental variables. Several electrode types were used for the charging and discharging procedures. The results led to know the experimental conditions for the heterocharge and homocharge accumulating and decreasing. The electronic structure parameters of polyethylene such as trap level, density of traps, hopping length, mobility, trap time constants were deduced. A method for evaluating the local electric field inside the electret is proposed.

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.542-545
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• 1990

Texture provides an important source of information about the local orientation of visible surfaces. In this study the 3D shape of a textured surface is recovered from its perspective projection image on the assumption that the texture is homogeneously distributed. To recover 3D structure, the distorting effects of the perspective projection must be distinguished from properties of the texture. In this study, paraperspective projection, approximation of perspective projection, has employed.

• Proceedings of the Korean Magnestics Society Conference
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• 2011.12a
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• pp.25-26
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• 2011

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1983-1985
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• 1999

The dielectric constant of a monolayer on a material surface was calculated with consideration of the local field acting on polar molecules with a permanent dipole moment, and the interaction working between the molecules and a material. It is revealed that the dielectric relaxation time r of monolayers in the isotropic polar orientational phase is determined using a linear relationship between the monolayers compression speed a and the molecular area. The dielectric relaxation time of phospholipid monolayers was examined on the basis of analysis developed here.