• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.645-654
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• 2005

This paper presents a nonlinear finite element procedure for the analysis of reinforced and prestressed concrete shells using the four-node quadrilateral flat shell element with drilling rotational stiffness. A layered approach is used to discretize, through the thickness, the behavior of concrete, reinforcing bars and tendons. Using the smeared-crack method, cracked concrete is treated as an orthotropic nonlinear material. The steel reinforcement and tendon are assumed to be in a uni-axial stress state and to be smeared in a layer. The constitutive models, which cover the loading, unloading, and reloading paths, and the developed finite element procedure predicts with reasonable accuracy the behavior of reinforced and prestressed concrete shells subjected to different types of loading. The proposed numerical method fur nonlinear analysis of reinforced and prestressed concrete shells is verified by comparison with reliable experimental results.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.297-300
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• 2006

In this paper, the EM wave absorbers were designed and fabricated for X-band sensors using Carbon of dielectric material with CPE. The complex relative permittivity of samples is calculated by the measured S-parameter data. We simulated the double-layered type EM wave absorber with broad bandwidth using the measured complex relative permittivity by changing the thickness and layer, which was fabricated based on the simulated design. The fabricated EM wave absorber consist of 1mm first layer sheet facing metal with Carbon composition ratio 70 vol% and 1.5 mm second layer sheet with Carbon composition ratio 60 vol%. The comparisons of simulated and measured results are good agreement. As a result, the optimized absorption ability of double-layered type EM wave absorber with thickness of 2.5 mm is higher than 10 dB from 7.8 GHz to 13.3 GHz.

• KIEAE Journal
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• v.7 no.5
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• pp.53-58
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• 2007

In order to predict the indoor air pollutant, the VOCs emission rate is used through small chamber in the design process. However, the small chamber method has limitations as the convective mass transfer coefficient, the most important factor when predicting VOCs contamination of indoor air, is different between the small chamber result and the measured data in the actual building. Furthermore, the existing studies which analyzed mass transfer coefficient in the small chamber were directed on the small chambers developed at the time and FLEC(Field and Laboratory Emission Cell), thus, are different from the current small chamber which has been changed with improvements. The purpose of this study is to determine the emission rate of pollutant in multi-layered building materials, and predict the indoor pollutant concentration through the CFD(Computational of Fluid Dynamics) and CRIAQ2 based on the mass transfer coefficient on singled-layered building material by using the current small chamber widely used in Korea. Futhermore, this study used the new convective mass transfer coefficient(hm') which indicates the existing convective mass transfer coefficient(hm) including VOC partition coefficient(k). Also, formaldehyde was selected as target pollutant.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.180-186
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• 2018

We report the discovery of Li-rich $Li_{1+x}[(Ni_{0.225}Co_{0.15}Mn_{0.625})_{1-y}V_y]O_2$ as a cathode material for rechargeable lithium-ion batteries in which a small amount of tetravalent vanadium ($V^{4+}$) is selectively and completely incorporated into the manganese sites in the lattice structure. The unwanted oxidation of vanadium to form a $V_2O_5-like$ secondary phase during high-temperature crystallization is prevented by uniformly dispersing the vanadium ions in coprecipitated $[(Ni_{0.225}Co_{0.15}Mn_{0.625})_{1-y}V_y](OH)_2$ particles. Upon doping with $V^{4+}$ ions, the initial discharge capacity (>$275mA\;h\;g^{-1}$), capacity retention, and voltage decay characteristics of the Li-rich layered oxides are improved significantly in comparison with those of the conventional undoped counterpart.

• Korean Journal of Materials Research
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• v.33 no.5
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• pp.222-228
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• 2023

Transition metal oxides formed by a single or heterogeneous combination of transition metal ions and oxygen ions have various types of crystal structures, which can be classified as layered structures and non-layered structures. With non-layered structures, it is difficult to realize a two-dimensional structure using conventional synthesis methods. In this study, we report the synthesis of cobalt oxide into wafer-scale nanosheets using a surfactant-assisted method. A monolayer of ionized surfactant at the water-air interface acts as a flexible template for direct cobalt oxide crystallization below. The nanosheets synthesized on the water surface can be easily transferred to an arbitrary substrate. In addition, the synthesizing morphological and crystal structures of the nanosheets were analyzed according to the reaction temperatures. The electrochemical properties of the synthesized nanosheets were also measured at each temperature. The nanosheets synthesized at 70 ℃ exhibited higher catalytic properties for the oxygen evolution reaction than those synthesized at other temperatures. This work suggests the possibility of changing material performance by adjusting synthesis temperature when synthesizing 2D nanomaterials using a wide range of functional oxides, resulting in improved physical properties.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.3
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• pp.169-181
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• 2011

In this present paper, a comprehensive drain current model incorporating the effects of channel length modulation has been presented for multi-layered gate material engineered trapezoidal recessed channel (MLGME-TRC) MOSFET and the expression for linearity performance metrics, i.e. higher order transconductance coefficients: $g_{m1}$, $g_{m2}$, $g_{m3}$, and figure-of-merit (FOM) metrics; $V_{IP2}$, $V_{IP3}$, IIP3 and 1-dB compression point, has been obtained. It is shown that, the incorporation of multi-layered architecture on gate material engineered trapezoidal recessed channel (GME-TRC) MOSFET leads to improved linearity performance in comparison to its conventional counterparts trapezoidal recessed channel (TRC) and rectangular recessed channel (RRC) MOSFETs, proving its efficiency for low-noise applications and future ULSI production. The impact of various structural parameters such as variation of work function, substrate doping and source/drain junction depth ($X_j$) or negative junction depth (NJD) have been examined for GME-TRC MOSFET and compared its effectiveness with MLGME-TRC MOSFET. The results obtained from proposed model are verified with simulated and experimental results. A good agreement between the results is obtained, thus validating the model.

• Bulletin of the Korean Chemical Society
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• v.27 no.10
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• pp.1587-1592
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• 2006

We report the preparation, structure and magnetic properties of a new pillared complex, copper(II) hydroxy-1,4-butanedisulfonate, $Cu_2(OH)_3(O_3SC_4H_8SO_3)_{1/2}$. The titled compound was obtained by anion exchange, using copper hydroxyl nitrate $(Cu_2(OH)_3NO_3)$ as the starting material. According to the XRD data, this compound exhibits a pillared layered structure with organic layers tilted between the copper hydroxide layers with a tilt angle of $21.8^{\circ}$. FTIR spectroscopy confirms total exchange of nitrate by the sulfonate and indicates that the sulfonate functions are linked to the copper(II) ions with each aliphatic chain bridging the adjacent hydroxide layers. According to the dc and ac magnetic measurements, the title compound is a metamagnet consisting of spin-canted antiferromagnetic layers, with a Neel temperature of 11.8 K.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.591-602
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• 2009

The Compton backscatter technique has been applied to lap-joint in aircraft structure in order to determine mass loss due to exfoliative corrosion of the aluminum alloy sheet skin. The mass loss of each layer has been estimated from Compton backscatter A-scan including the aluminum sheet, the corrosion layer, and the sealant. A Compton backscattering imaging system has been also developed to obtain a cross-sectional profile of corroded lap-splices of aging aircraft using a specially designed slit-type camera. The camera is to focus on a small scattering volume inside the material from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the layered structure is scanned by moving the scattering volume through the thickness direction of the specimen. The theoretical model of the Compton scattering based on Boltzmann transport theory is presented for quantitative characterization of exfoliative corrosion through deconvolution procedure using a nonlinear least-square error minimization method. It produces practical information such as location and width of planar corrosion in layered structures of aircraft, which generally cannot be detected by conventional NDE techniques such as the ultrasonic method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.9
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• pp.805-812
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• 2011

This study investigated the characteristics of heavy-weight floor impact sounds of box-frame type structure using 1:10 scale model. Ten types of floor structures(bare slabs and floating floors) were evaluated in terms of dynamic stiffness and loss factor. Floor vibrations and radiated sounds generated by simulated impact source were also measured. The results showed that the bakelite was appropriate for simulating concrete slab in the 1:10 scale model, and surface velocity and sound pressure level of concrete slab measured from the scale model showed similar tendencies with the results from in-situ in frequency domain. It was also found that dynamic behaviors of layered floor structures in the 1:10 scale model were similar to those in a real scale. Therefore, the use of 1:10 scale model would be useful for evaluating the heavy-weight floor impact sound insulation of layered floor structures when the frequency-dependent dynamic properties of each material are known.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.180-181
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• 2006

As a rule, high temperature superconducting coated conductors have multi-layered buffers consisting of seed, diffusion barrier and cap layers. Multi-buffer layer deposition requires longer fabrication time. This is one of main reasons which increases fabrication cost Thus, single buffer layer deposition seems to be important for practical coated conductor process. In this study, a single layered buffer deposition of $CeO_2$ for low cost coated conductors has been tried using thermal evaporation technique 100nm-thick $CeO_2$ layers deposited by thermal evaporation were found to act as a diffusion layer. $0.4{\mu}m$-thick SmBCO superconducting layers were deposited by thermal co-evaporation on the $CeO_2$ buffered Ni-W substrate. Critical current of 118A/$cm^2$ was obtained for the SmBCO coated conductors.