• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1808-1813
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• 2005

In this paper, we present the finger tip tactile sensor which can detect contact normal force as well as slip. The developed sensor is made of two different materials, such as polyvinylidene fluoride(PVDF) that is known as piezoelectric polymer and pressure variable resistor ink. In order to detect slip to surface of object, a PVDF strip is arranged along the normal direction in the robot finger tip and the thumb tip. The surface electrode of the PVDF strip is fabricated using silk-screening technique with silver paste. Also a thin flexible force sensor is fabricated in the form of a matrix using pressure variable resistor ink in order to sense the static force. The developed tactile sensor is physically flexible and it can be deformed three-dimensionally to any shape so that it can be placed on anywhere on the curved surface. In addition, we developed a tactile sensing system by miniaturizing the charge amplifier, in order to amplify the small signal from the sensor, and the fast signal processing unit. The sensor system is evaluated experimentally and its effectiveness is validated.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.373-376
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• 2008

New glass compositions for lead free, low temperature sealing glass frit was examined in $ZnO-V_2O_5-P_2O_5$ glass system which can be used sealing material for PDP to be made of soda lime glass substrates. Among many glass compositions, KFS-C glass showed low glass transition point (Tg) and good fluidity and adhesion characteristics when it was tested by flow button method at low temperature of $420^{\circ}C$. Its Tg was $317^{\circ}C$ and thermal expansion coefficient (CTE) was $70{\times}10^{-7}/K$. The glass frit was mixed with an organic vehicle to make a paste and it was dispensed and sealed with soda lime glass substrates at $420^{\circ}C$ for 10min. Sealed glass panels also showed good adhesion strength even sealed at low temperature of $420^{\circ}C$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.4
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• pp.139-143
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• 2005

For application of carbon nano-tube (CNT) as a counter electrode materials of dye-sensitized solar cell (DSSC), the electrochemical behavior of CNT electrode was studied, employing cyclic-voltammetry (C-V) and impedance spectroscopy. Fabrication of CNT-paste and formation of CNT-counter electrode for characteristic measurement have been carried out using ball-milling and doctor blade process, respectively. Unit cell for measurements was assembled using Pt electrode, CNT electrode, and iodine-embedded electrolyte. Field emission-scanning electron microscopy (FE-SEM) was used for structural investigation of CNT powder and electrode. Sheet resistance of electrode was measured with 4-point probe method. Electrochemical properties of electrode, C-V and impedance spectrum, were studied, employing potentiogalvanostat (EG&G 273A) and lock in amplifier (EG&G 5210). As a results, the sheet resistance of CNT electrode is almost similar to that of F-doped SnO2 (FTO) coated glass substrate as approximately 10 ohm/sq. From C-V and impedance spectroscopy measurements, it was found that CNT electrode has high reaction rate and low interface reaction resistance between CNT surface and electrolyte. These results provides that CNT electrode were superior to that of conventional Pt electrode. Particularly, the reaction rate in the CNT electrode is about thrice high than Pt electrode. Therefore. CNT electrode is to be good candidate material for counter electrode in DSSC.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.78-82
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• 2000

Although alumina aggregates have been used as refractory aggregates due to the improved mechanical properties of refractories as a result of the low contraction of alumina aggregates, the aggregates have a difficulty in fabrication due to its low sinterability. Two types of alumina aggregates and a fused alumina aggregate containing transient liquid forming additives are prepared to investigate the sintering characteristics of aggregates. $Al_2O_3$rich composition in the $Al_2O_3$-MgO-$SiO_2$(-$TiO_2$) system is chosen for the transient liquid phase sintering and the final recrystallized bonding phase between grains inside the fused alumina aggregates is found to be a needle-like mullite phase. The flexural strength of alumina bars, reaction-bonded using the paste having a composition of $Al_2O_3$-MgO-$SiO_2$-$TiO_2$, is about 78 MPa, which is one half value of that of pure alumina.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.10-18
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• 1974

The hydration at $23^{\circ}C$ between $Ca(OH)_2$ and siliceous materials with various compositions of silica gel and quartz were studied in paste state, and also diatomite was empolyed as another form of silica. The effect of the structural state of silica on the pozzolanic reactivity was investigated by X-ray, DTA, electron microscopy, and chemical analysis. The results obtained were as follows. (1) The molar ratio of $Ca(OH)_2$ to silica gel(C/Sg) being changed in 0.49, 0.81 and 1.22, the free $Ca(OH)_2$ was disappeared within six hours, three days and two weeks respectively and ill-crystallized CSH(I) was formed. However, in the case fo molar ratio of C/Sg=2.45, almost lime was remained uncombinedly after twenty four weeks yet. (2) Though the molar ratio C/Sg of diatomite was 0.71, the hydration was stabilized at three weeks and the result exhibited very peculiar characteristics from silica gel. (3) Pozzolanic reactivity of quartz was negligible, but $\alpha$-cristobalite in diatomite showed appreciable reactivity. (4) The thermal curves showed the exothermic peaks in the range 830 to $930^{\circ}C$ and lower broad peaks at high temperature in the initial steps of hydration, transfered to lower temperature with sharp peaks by proceeding of hydration. (5) The samples containing more silica gel exhibited higher pozzolanic reactivity and martar strength, but the diatomite gave remarkable result for them and they were matched to the strength development rate.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.391-399
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• 2015

This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.5-8
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• 2009

In this paper, a high-quality low-temperature co-fired ceramic (LTCC) solenoid inductor using a solder ball and an air cavity on a silicon wafer for three-dimensional (3-D) system-in-package (SiP) is proposed. The LTCC multi-layer solenoid inductor is attached using Ag paste and solder ball on a silicon wafer with the air cavity structure. The air cavity is formed on a silicon wafer through an anisotropic wet-etching technology and is able to isolate the LTCC dielectric loss which is equivalent to a low k material effect. The electrical coupling between the metal layer and the LTCC dielectric layer is decreased by adopting the air cavity. The LTCC solenoid inductor using the solder ball and the air cavity on silicon wafer has an improved Q factor and self-resonant frequency (SRF) by reducing the LTCC dielectric resistance and parasitic capacitance. Also, 3-D device stacking technologies provide an effective path to the miniaturization of electronic systems.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.51-56
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• 2000

Fly ash used as a cement replacement material increases the long term strength and also improves the durability of concrete and mortar. However, the use of fly ash is a little in spite of great benefit. In order to increase the consumption of fly ash, it has to be used as a cement replacement materials in the production of mortar and concrete, and the reduction of early strength development due to the use of fly ash also has to be diminished. In this study, many chemical compounds which accelerate the early strength was investigated. The $Na_2$$SO_4$, $K_2$$SO_4$, Triethanolamine were selected and applied to the production of mortar. It was found that they enhance the early strength development of mortar(1, 3day) and decrease the amount of $Ca(OH)_2$, and also increase the production of ettringite. According to the results of mercury instruction test, the pores ranged from 0.01 $\mu\textrm{m}$ to 5$\mu\textrm{m}$ were decreased and it was also found in the analysis of X ray and SEM that fly ash increases the amount of ettringite at early ages.

• Current Photovoltaic Research
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• v.4 no.4
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• pp.140-144
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• 2016

In this paper, core-shell structure of nickel/gold (Ni/Au) conductive layer on poly-methyl-methacrylate (PMMA) micro-ball was fabricated and its conduction property was investigated. Firstly, PMMA micro-ball was synthesized by using dispersion polymerization method. Size of the ball was $2.8{\mu}m$ within ${\pm}7%$ deviation, and appropriate elastic deformation of the PMMA micro-ball ranging from 31 to 39% was achieved under 3 kg pressure. Also, 200 nm thick Ni/Au conductive layer was fabricated on the PMMA micro-ball by uniformly depositing with electroless-plating. Adhesion of the conductive layer was optimized with help of surface pre-treatment, and the layer adhered without peeling-off despite of thermal expansion by collision with accelerated electrons. Composite paste containing core-shell structured particles well cured at low temperature of $130^{\circ}C$ while pressing the test chip onto the substrate to make electrical contact, and electrical resistance of the conductive layer showed stable behavior of about $6.0{\Omega}$. Thus, it was known that core-shell structured particle of the Ni/Au conductive layer on PMMA micro-ball was feasible to flexible electronics.

• Toxicological Research
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• v.29 no.4
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• pp.293-298
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• 2013

A method of detecting lead was developed using square wave anodic stripping voltammetry (SWASV) with DNA-carbon nanotube paste electrode (CNTPE). The results indicated a sensitive oxidation peak current of lead on the DNA-CNTPE. The curves were obtained within a concentration range of 50 $ngL^{-1}-20mgL^{-1}$ with preconcentration time of 100, 200, and 400 sec at the concentration of $mgL^{-1}$, ${\mu}gL^{-1}$, and $ngL^{-1}$, respectively. The observed relative standard deviation was 0.101% (n = 12) in the lead concentration of 30.0 ${\mu}gL^{-1}$ under optimum conditions. The low detection limit (S/N) was pegged at 8 $ngL^{-1}$ ($2.6{\times}10^{-8}M$). Results showed that the developed method can be used in real-time assay in vivo without requiring any pretreatment and pharmaceutical samples, and food samples, as well as other materials requiring water source contamination analyses.