• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.167-174
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• 2010

In this study, the optimal position for the backrest pivot of an office chair was investigated by evaluating its performance in terms of the lumbar support and sliding distance of the back from the backrest during tilting motions. The simulation was performed using a mathematical model, which included a human body and a chair. Forty-two backrest pivot points were selected on the sagittal plane around the hip joint of a sitting model. A motion analysis study was also performed using a prototype of an office chair (A-type) with a backrest pivot located on the hip joint of a normal Korean model and a typical office chair (B-type) with its pivot located under the seat. The simulation results showed that both the lordosis angle and the slide distance of the back were minimized when the backrest pivot was positioned close to the hip joint. The experimental results showed that the slide distance and gap between the sitter's lumbar and the backrest was smaller with the A-type than the B-type. Based on the simulation and experimental results, it can be concluded that the backrest can support the sitter's lumbar area more effectively as the pivot position for reclining approaches closer to the hip joint. In this position, the sitter can maintain a comfortable and healthy sitting posture. This paper presents the methods and guidelines for designing an office chair with ergonomic considerations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.373-381
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• 2016

In this study, we investigate the characteristics of the drag reduction of a circular cylinder having a detached splitter plate at the wake side. We measure the fluid force on a circular cylinder and visualize the field using particle image velocimetry (PIV) with a high Reynolds number, Re = 10,000. The experimental paraeters used were the width ratios (H/B = 0.5~1.5) of splitters to the prism width and the gap ratios (G/B = 0~2) between the prism and the splitter plate. The drag-reduction rate of the circular cylinder increased with H/B in the case of the same G/B, and it increased and then decreased with G/B in the case of the same H/B. The vortices of the opposite direction on the upper and lower sides of the detached splitter plate were generated by installing the plate. Reverse flow was caused by the vortices at the wake region of the circular cylinder, and the drag of the circular cylinder was decreased by the reverse flow.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.537-543
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• 2013

In this study, the push-pull structure polymer for organic photo voHaics (OPVs) was synthesized and characterized. The poly{4,8-didodecyloxybenzo[1,2-b;3,4-b]dithiophene-alt-5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (PDBDT-TBTD) was synthesized by Stille coupling reaction using the benzothiadiazole (BTD) derivative as an electron acceptor and benzodithiophene (BDT) derivative as an electron donor. The structure of monomers and polymers was identified by $^1H-NMR$ and GC-MS. The optical, physical and electrochemical properties of the conjugated polymer were identified by GPC, TGA, UV-Vis and cyclic voltammetry. The number average molecular weight ($M_n$) and initial decomposition temperature (5% weight loss temperature, $T_d$) of PDBDT-TBTD were 6200 and $323^{\circ}C$, respectively. The absorption maxima on the film was about 599 nm and the optical band gap was about 1.70 eV. The structure of device was ITO/PEDOT : PSS/PDBDT-TBTD : $PC_{71}BM/BaF_2/Ba/Al$. PDBDT-TBTD and $PC_{71}BM$ were blended with the weight ratio of 1:2 which were then used as an optical active layer. The power conversion efficiency (PCE) of fabricated device was measured by solar simulator and the best PCE was 2.1%.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.2
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• pp.67-74
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• 2009

In this paper, the multi-band antenna with CPWG(Coplanar Waveguide with Ground) feed for telematics mobile devices is designed and fabricated. The proposed antenna improves the return loss characteristic by using open-circuited stub matching and rectangular slot in the radiation patch. In addition, CPWG structure makes up for the drawback of the CPW which is variation of impedance matching according to the gap variation of the feed line and the ground. The fabricated antenna has 1.4GHz ($1.43GHz{\sim}2.83GHz$, 65%) band width on -10dB (VSWR<2) and the maximum gains are 0.8dBi, 1.34dBi, 2.41dBi, 2.53dBi, 2.6dBi and 1.51dBi on each resonant frequency that are GPS $(1.564GHz{\sim}1.585GHz)$, PCS/DCS $(1.710GHz{\sim}1.984GHz)$, WCDMA $(2.170GHz{\sim}2300GHz)$, Bluetooth/Wi-Fi/WLAN $(2.4GHz{\sim}2.483GHz)$, WiBro $(2.3GHz{\sim}2.4GHz)$, SDMB $(2.605GHz{\sim}2.655GHz)$. It also has an omni-directional radiation pattern of H-Plane.

• The Journal of the Petrological Society of Korea
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• v.15 no.1 s.43
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• pp.39-48
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• 2006

U-Pb ages were determined from the granitic rocks from central and northeastern parts of Yeongnam massif. Porphyritic granite of Seosang-myeon, Hamyang-gun near the boundary with Anui-myeon shows age of $225.4{\pm}4.1Ma$. Foliated granodiorites of Anui-myeon, Hamyang-gun and Sinwon-myeon, Geochang-gun are $195.6{\pm}1.8Ma$ and $194.2{\pm}2.4Ma$ old respectively. Granites from Hari-myeon and Buksang-myeon of Geochang-gun show almost identical ages of $198.4{\pm}2.5Ma$ and $194.6{\pm}2.6Ma$ respectively, while foliated granodiorite of Yeongju shows an age ot $171.3{\pm}2.3Ma$. Combining with previously reported results, Triassic granitoids were emplaced almost identically at ca. 225 Ma throughout the areas of Hamyang and Sangju oi Yeongnam massif and Baengnok, Jeomchon and Goesan of Okcheon metamorphic belt. There were significant gap of non-magmatism before the resume of granitic activities over the large areas of Hamyang-gun, Geochang-gun, Gimcheon-si and Seongju-gun from Triassic-Jurassic boundary to early Jurassic, 200-194 Ma. Igneous activity within the Yeongnam massif of this period has not been reported from the Okcheon belt or Gyeonggi massif and may reflect distinct tectonic environment. Around 170 Ma, when Yeongju granodiorite was emplaced, there were active granitic magamtism throughout the Yeongnam massif, Okcheon belt and also Gyeonggi massif.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.1
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• pp.6-13
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• 2010

In this study, Ga-doped ZnO (GZO) thin films have been fabricated on Eagle 2000 glass substrates at various substrate temperatures $100{\sim}400^{\circ}C$ and thin film thickness by RF magnetron sputtering in order to investigate the structural, electrical, and optical properties of the GZO thin films. It is observed that all the thin films exhibit c-axis orientation and a (002) diffraction peak only. The GZO thin films, which were deposited at $T=300^{\circ}C$ and 400 nm, shows the highest (002) orientation, and the full width at half maximum (FWHM) of the (002) diffraction peak is $0.4^{\circ}$. AFM analysis shows that the formation of relatively smooth thin films are obtained. The lowest resistivity ($8.01{\times}10^{-4}\;{\Omega}cm$) and the highest carrier concentration ($3.59{\times}10^{20}\;cm^{-3}$) are obtained in the GZO thin films deposited at $T=300^{\circ}C$ and 400 nm. The optical transmittance in the visible region is approximately 80 %, regardless of process conditions. The optical band-gap shows the slight blue-shift with increase in doping which can be explained by the Burstein-Moss effect.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.5
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• pp.15-20
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• 2007

We fabricated ZnO thin films on quartz substrate using pulsed laser deposition method and investigated structural and optical properties of ZnO thin films with various substrate temperatures. Regardless of the substrate temperature variation, all ZnO thin films had grown to (002) and the thin film deposited at 400 $^{\circ}C$ exhibited an excellent crystallinity having 0.24$^{\circ}$ of Full-Width-Half-Maximum (FWHM). In the result of photoluminescence property, UV and deep-level emission peaks were observed in all ZnO films and the emission peaks were changed with various substrate temperatures. An highest UV emission was exhibited on the specimen deposited at 400 $^{\circ}C$ and the FWHM of UV peak was 14 nm. The optical transmittance was about 85 % in visible region regardless of the substrate temperature. The comparison result of the bandgap energies obtained from optical transmittance and UV emission centers, the two values were about the same. From these results, it is found that UV emission center has close relationship with near band edge emission of ZnO thin film.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.5
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• pp.1-7
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• 2007

AZO thin films have been fabricated on quartz substrate with various Al doping concentrations and annealing temperatures by sol-gel method. The bset condition of (002) orientation and smooth surface (rms = 1.082 nm) is obtained for the AZO thin film doped with 1 mol % Al and annealed at 550 $^{\circ}C$. The optical transmittance of AZO thin films is higher than 80 % in the visible region. We observe that the energy band gap extends with increasing the Al doping concentration. This phenomenon is due to the Burstein-Moss effect. Through the measurement of Hall effect, it is observed that the AZO thin film has larger carrier concentration and smaller electrical resistivity than the pure ZnO thin film. However, the AZO thin film shows the decrease of carrier concentration and the increase of resistivity with the increase of Al concentration, that is due to the segregation of Al at grain boundaries. The maximum carrier concentration of $1.80{\times}10^{19}\;cm^{-3}$ and the minimum resistivity of 0.84 ${\Omega}cm$ are obtained for the AZO thin film doped with 1 mol % Al and annealed at 550 $^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.8
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• pp.891-898
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• 2008

In this paper, we have studied on the possibilities of the biomaterial detection using single-walled carbon nanotube (SWNT) based on interdigital capacitors. For the four different configurations, such as interdigital capacitor, SWNT in the $5\;{\mu}m$ gap interdigital capacitor, biotinlated SWNT, and biotin and sreptavidin immobilization cases, the resonant frequency has been measured as 10.02 GHz, 11.02 GHz, 10.82 GHz, and 10.22 GHz, respectively. Assuming that the resonant frequency reflects the capacitance changes due to binding of two-different permittivity biomaterials, we have suggested an equivalent circuit model based on measured results, confirming the capacitance changes. For biotinlated SWNT and biotin-streptavidin immobilization cases, the capacitances are $C_b=0.55\;pF$ and $C_s=0.95\;pF$. In this work, we experimentally demonstrated that the specific biomaterial binding causes the capacitance change and therefore this gives rise to resonant frequency. In conclusion, we confirmed the sufficient possibility as CNT biosensor because an analyte biomaterial(streptavidin) binding arouses a considerable resonant frequency change.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.443-451
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• 2010

This paper describes a fully integrated CMOS low-IF mobile-TV RF tuner for Band-III T-DMB/DAB applications. All functional blocks such as low noise amplifier, mixers, variable gain amplifiers, channel filter, phase locked loop, voltage controlled oscillator and PLL loop filter are integrated. The gain of LNA can be controlled from -10 dB to +15 dB with 4-step resolutions. This provides a high signal-to-noise ratio and high linearity performance at a certain power level of RF input because LNA has a small gain variance. For further improving the linearity and noise performance we have proposed the RF VGA exploiting Schmoock's technique and the mixer with current bleeding, which injects directly the charges to the transconductance stage. The chip is fabricated in a 0.18 um mixed signal CMOS process. The measured gain range of the receiver is -25~+88 dB, the overall noise figure(NF) is 4.02~5.13 dB over the whole T-DMB band of 174~240 MHz, and the measured IIP3 is +2.3 dBm at low gain mode. The tuner rejects the image signal over maximum 63.4 dB. The power consumption is 54 mW at 1.8 V supply voltage. The chip area is $3.0{\times}2.5mm^2$.