• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.3-6
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• 1996

The Ultra-high molecular weight polyethylene (UHMWPE) is exclusivity used as the articulation component with metal or ceramic materials in artificial joint prosthesis because of its good mechanical properties. In the long term however, wear of UHMWPE causes complex problems and hence causes loosening of He prosthesis. In this study, we tried to enhance the wear property of UHMWPE by attaching a hydrophilic graft on the UHMWPE surface and by improving surface hardness without deteriorating the mechanical properties of UHMWPE. This was achieved by ion implantation and by ${\gamma}$-irradiation to the surface in acrylic acid solution and by photo-polymerization in divinylbenzen (DVB), diallysophthalate (DAIP) solution. The wear test was performed by a wear testing machine of ball-on-disk type devised by the authors. The UHMWPE with hydrophlic surface and increased surface hardness developed by above treatments showed less volumetric wear.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.45-51
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• 2014

Luby transform (LT) codes are a class of ratelss codes, and they have capability of generating infinite length of parities with a given information length. These rateless codes can be effectively utilized to provide broadcasting and multicasting services where each user is in a different channel condition. For this reason, there have been a number of researches on the application of rateless codes for satellite systems. In this paper, by considering the current research status on rateless codes, we present VHLD implementation results of LT codes, for future hardware implementation for satellite systems. The results demonstrated in this paper can be utilized as a basic information on efficient utilization of rateless codes in the future satellite systems.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1365-1368
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• 2002

OFDM은 제4세대 변조기술로 일컬어지는 방식이다. 이는 최근 유럽에서 디지털 오디오 방송(DAB)과 디지털 비디오 방송(DVB)에 표준이 되었으며, IEEE 802.11a 무선 LAN 에서도 이 방식을 채택했고, ADSL, VDSL 등에서도 사용되어지고 있다. 본 논문에서는 이러한 OFDM 방식의 핵심이라고 할 수 있는 64포인트 FFT(Fast Fourier Transform)하드웨어 프로세서의 여러 가지의 구현된 예를 비교 분석하고, 가장 효율적인 방법인 Radix-2 SDF(Singlepath Delay Feedback)[1] 방법을 개선하여 새로운 구조를 제안하였다. 동일한 속도 성능을 가지는 여러구조 중에서 적은 수의 지연소자를 활용하여 FFT 크기를 작게 한 것이 SDF 방식으로 가장 널리 사용되고 있다. 본 논문에서는 SDF 방식이 내부적으로 4개의 복소곱셈기를 필요로 하는데 비해 2개의 복소곱셈기만을 사용하는 구조로 변형하고 컨트롤을 조절하여 새로운 구조를 설계하였다. 구현한 결과, FFT에서 전체 구조의 약 80%를 차지하는 복소곱셈기의 수를 절반으로 줄여 FFT 하드웨어 크기를 SDF 방식의 60% 정도로 줄일 수 있게 되었고, 이러한 구현방식은 64포인트 FFT만이 아닌 더 큰 크기의 FFT를 구현함에 있어서도 동일하게 적용할 수 있으며 현재 국내외에 발표된 논문 중 성능 대 면적비가 가장 우수한 구조이다.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2007.11a
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• pp.93-114
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• 2007

Vaccinium uliginosum L. (VU) is a flowering plant in the genus Vaccinium has berry fruit. This study was performed to investigate the effect of water extract of Vaccinium uliginosum L. and fractions on inhibition of melanogenesis and wrinkle formation. One hundred grams of the Vaccinium uliginosum L. was extracted with 2,000 mL of water ($90^{\circ}C$, 16h, 2 times). The water extracts were lyophilized and stored at $4^{\circ}C$ until used. Vaccinium uliginosum L. extracts showed scavenger activities on DPPH radical, superoxide anion radical, hydroxyl radical, hydrogen peroxide and singlet oxygen radical, dose dependently. And VU extract and fractions reduced melanin contents on B16F10 melanoma and inhibited the expression of melanogenesis-related proteins, tyrosinase, tyrosinase-related protein (TRP-1) and dapachrometa utomerase (Dct, TRP-2). Moreover VU extract and fractions stimulated procollagen production and inhibited MMP-1 production in human fibroblast. And it decreased degree of wrinkle formation in hairless mouse skin that induced by DVB irradiation for 9 weeks. From the above results, it is possible that Vaccinium uliginosum L. may be developed to be the health functional food and functional cosmetics that have anti-melanogenesis and anti-wrinkle effect.

• Journal of Information Processing Systems
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• v.15 no.3
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• pp.670-681
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• 2019

Orthogonal frequency division multiplexing (OFDM) is a system which is used to encode data using multiple carriers instead of the traditional single carrier system. This method improves the spectral efficiency (optimum use of bandwidth). It also lessens the effect of fading and intersymbol interference (ISI). In 1995, digital audio broadcast (DAB) adopted OFDM as the first standard using OFDM. Later in 1997, it was adopted for digital video broadcast (DVB). Currently, it has been adopted for WiMAX and LTE standards. In this project, a Verilog design is employed to implement an OFDM transmitter (DAC block) and receiver (FFT and ADC block). Generally, OFDM uses FFT and IFFT for modulation and demodulation. In this paper, 16-point FFT decimation-in-frequency (DIF) with the radix-2 algorithm and direct summation method have been analyzed. ADC and DAC in OFDM are used for conversion of the signal from analog to digital or vice-versa has also been analyzed. All the designs are simulated using Verilog on ModelSim simulator. The result generated from the FFT block after Verilog simulation has also been verified with MATLAB.

• ETRI Journal
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• v.41 no.3
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• pp.308-315
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• 2019

Due to its high spectrum efficiency, 64-amplitude phase-shift keying (64-APSK) is one of the primary technologies used in deep space communications and digital video broadcasting through satellite-second generation. However, 64-APSK suffers from considerable computational complexity because of the de-mapping method that it employs. In this study, a low-complexity de-mapping method for (4 + 12 + 20 + 28) 64-APSK is proposed in which we take full advantage of the symmetric characteristics of each symbol mapping. Moreover, we map the detected symbol to the first quadrant and then divide the region in this first quadrant into several partitions to simplify the formula. Theoretical analysis shows that the proposed method requires no operation of exponents and logarithms and involves only multiplication, addition, subtraction, and judgment. Simulation results validate that the time consumption is dramatically decreased with limited degradation of bit error rate performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.4 no.3
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• pp.183-189
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• 2009

In this paper, we propose RF front-end architecture using hybrid conversion method to receive broadband signal. The validity is verified by design, fabrication and experiment. The proposed RF front-end architecture due to up-conversion block improves the deficiency of performance deterioration to be generated through harmonic signal and image signal conversion in the conventional RF front-end, and improves the deficiency of the complexity that is from to adopt a multiple local oscillators for the generation of wideband LO signal in the conventional RF front-end by applying the principle that tuning bandwidth is multiplied at sub-harmonic mixer. Manufactured circuits satisfy the deduced design specification and target standard with gain above 80 dB, noise figure below 6.0 dB and IIP3 performance above -5.0 dBm for the condition of the minimum gain in RF front-end.

• Journal of the Korean Chemical Society
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• v.42 no.2
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• pp.190-196
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• 1998

A new sampling and size exclusion chromatography (SEC) method for the analysis of underivatized cellulose are established. In this method, cellulose materials are first dissolved in N-methylmorpholine N-oxide (NMMO) and diluted by adding dimethyl sulfoxide (DMSO) to make the sample solutions of about 0.1% in 50/50 NMMO/DMSO (w/w). Sample solutions are analyzed using a glucose-treated divinylbenzene (DVB) SEC column and DMSO containing 0.05M LiBr and 2.5 blank as the eluant. The flow rate was constant at 1 mL/min and the whole SEC system including the column was heated at $80^{\circ}C$ to reduce the viscosity of DMSO. Addition of 0.05 M LiBr eliminated SEC baseline drifting, and addition of 2.5 blank seems to reduce the interaction between the sample and the column packing. SEC molecular weights were determined using a calibration curve constructed from a series of narrow pullulan standards, and they were used to measure the degree of degradation during two different pulp-to-sponge processings.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.938-945
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• 1996

The present studies are to describe the grafting reaction of styrene in various solvents to polypropylene fabric by the simultaneous method using Co-60. The influence of various factors such as absorbed dose, dose rate, type of solvent, acid and multifunctional monomer were evaluated. At constant absorbed dose, the grafting yield was found to be higher at low dose rate. The initial rate of grafting was found to be proportional to a 0.56 power of dose rate. The inclusion of mineral acid in the grafting solution led to an increase in radiation grafting yield at almost all monomer concentration examined. Multifunctional monomer was also effective to increase grafting yield. The addition of both acid and multifunctional monomer was found to accelerate the grafting yield much more than the separate addition of two additives.

• Journal of environmental and Sanitary engineering
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• v.15 no.1
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• pp.25-33
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• 2000

The new ion exchange resin was synthesized from chloromethylated styrene-1,4-divinylbenzene(DVB) with 1-aza-15-crown-5 macrocyclic ligand by substitution reaction. The effect of pH, time, dielectric constant of solvent and cross-linked of the matrix on the adsorption for $UO_2^{2+}$, $Ca^{2}$ and $Lu^{3+}$ was investigated. The metal ion was not adsorbed on the resins below pH 3 but above pH 4 fast adsorption behavior was showed. The optimum equilibrium time for adsorption of metallic ions was two hours. The adsorption selectivity determined in ethanol matrix was in increasing order $UO_2^{2+}>Ca^{2}>Lu^{3+}$. The adsorption power was in the order of 1%, 2%, 10% and 20% -crosslinked resin, but adsorption properties of resins decreased in proportion to the order of dielectric constant of solvents used. In addition, these metal ions could be separated in the column packed with 1% crosslinked resin by pH2.5 $HNO_3$ as an eluent.