• Journal of IKEEE
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• v.18 no.3
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• pp.320-327
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• 2014

Recently, Importance of power management circuit technology is increased with the development of portable electric devices. This paper presents a high performance DC-DC buck converter for mobile applications. Especially, presented design have low ripple voltages and driving capability of large load current. A designed voltage mode 2-phase DC-DC converter is implemented in a $0.35{\mu}m$ CMOS process, and the overall size is $2.35{\times}2.35mm^2$. The peak efficiency is 91% with a 4MHz frequency and the maximum load current is 4A.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.148-155
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• 2008

In wireless data communication systems, retransmission of an erroneous packet is inevitable due to the harsh communication environment. In this paper, an efficient retransmission scheme using cooperation from neighboring nodes is investigated. In the cooperative retransmission scheme, an erroneous packet is transmitted to the destination by cooperative nodes which have favorable channels. This cooperative retransmission scheme requires no a priori information of neighboring nodes and has no limitation on the number of cooperating nodes. Distributed beamforming is used to accommodate multiple cooperating nodes. Phase and frequency offsets of cooperating signals are extracted from the NACK message and used to co-phase retransmitted data packets. The outage probability of the cooperative retransmission scheme is analyzed for the case of perfect synchronization and when the offsets are estimated. To reduce the impact of the residual phase and frequency offsets in cooperating signals, a low-rate feedback scheme is also investigated. It is shown that improved outage probability and reduced packet error rate (PER) performance can be achieved even for long data packets. The proposed cooperative retransmission scheme is found to outperform simple retransmission by the source as well as decode-and-forward cooperation.

• KSBB Journal
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• v.16 no.4
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• pp.327-331
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• 2001

Catechin compounds from the Green tea cultivated in Bosung (Chollanamdo) were extracted using supercritical fluid and various additives, and analyzed by reversed-phase high performance liquid chromatography (RP-HPLC). The chromatographic column was packed with LiChrospher 100RP-18(15 $\mu$m), and water was used as the mobile phase with 0.05% phosphoric acid and acetonitrile. Gradient election was applied to separate EGCG by changing the mobile phase compositions. Comparing the extraction yield of three different types of supercritical fluids, pure CO$_2$, with additives of water and ethanol (5 wt,%), the extraction amount of EGCG was most abundant in the suprcritical CO$_2$with ethanol. However, more was extracted and pure higher purity was achieved by solvent extraction using ethanol.

• Journal of the Korean Chemical Society
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• v.34 no.1
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• pp.76-84
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• 1990

Optical isomers of dansyl amino acids were separated by a chiral mobile phase addition method. Two metha and para isomers of xylenyl-L-proline were prepared and used as the ligands of copper(Ⅱ) chelate to resolve the dansyl amino acids. Their elution behaviors were similar to those obtained from the addition of copper (Ⅱ) benzyl-L-proline chelate. The matrix effect of the mobile phase such as pH, concentration of buffer and compositions of organic solvent acetonitrile affected the optical resolution. The separation mechanism could be explained by a cis-trans effect of the ligand exchange reaction and hydrophobic interaction between the ternary complex and the stationary phase.

• Bulletin of the Korean Chemical Society
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• v.17 no.10
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• pp.949-951
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• 1996

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.20-22
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• 2003

본 논문에서는 Photonic Bandgap(PBG)를 공진 특성을 이용하여 마이크로파 발진기의 위상잡음을 줄이기 위한 기술을 제시한다. 마이크로스트립 라인으로 구현한 공진기는 낮은 Q(Quality factor)를 가진다. PBG를 적용했을 때 공진기의 Q값을 높여줌으로써 발진기의 위상잡음 특성이 향상됨을 보이고자 한다.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.32-39
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• 2009

Most mobile devices provide limited input interfaces in order to maximize the mobility and the portability. In this paper, the author proposes a small cubic-shaped tangible input interface which tracks the location, the direction, and the velocity using MEMS sensor technology to overcome the physical limitations of the poor input devices in mobile computing environments. As the preliminary phase for implementing the proposed tangible input interface, the prototype design and implementation methods are described in this paper. Various experiments such as menu manipulation, 3-dimensional contents control, and sensor data visualization have been performed in order to verify the validity of the proposed interface. The proposed tangible device enables direct and intuitive manipulation. It is obvious that the mobile computing will be more widespread and various kinds of new contents will emerge in near future. The proposed interface can be successfully employed for the new contents services that cannot be easily implemented because of the limitation of current input devices. It is also obvious that this kind of interface will be a critical component for future mobile communication environments. The proposed tangible interface will be further improved to be applied to various contents manipulation including 2D/3D games.

• Journal of the Korea Society of Computer and Information
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• v.13 no.5
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• pp.171-177
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• 2008

CBD(Component-based Development), which refers to the method of treating software as parts of a larger whole and developing new information systems through the assembly and synthesis of existing software, has been popular among many methods for developing software. However, CBD has limitations in the mobile environment which requires frequent requirements change and flexible process. To overcome those limitations, we propose an improved mobile development process based on the UML(Unified Modeling Language) components. Our Proposal is the simple development process implemented as three phase of component diagrams for the mobile system having quickly evolving technology and small-size project. Through the implementation of a mobile banking service with the proposed development process, we show that our proposal works efficiently for the requirements change and flexible development.

• KSBB Journal
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• v.14 no.1
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• pp.17-23
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• 1999

Studies were carried out to elucidate the effects of pressure, temperature and mobile phase composition on supercritical $CO_2$ chromatographic separations of paclitaxel, baccatin III, 10-deacetyl baccatin III, 7-epi-10-deacetyltaxol, cephalomanine, and 10-deacetyltaxol. High resolutions of paclitaxel, 10-deacetylbaccatin III, 10-deacetyltaxol were observed with optimized pressure, temperature, and mobile phase composition. The highest resolution between paclitaxel and 10-deacetylbaccain III was observed at 275 kg/$\textrm{cm}^2$, $40^{\circ}C$ with the mobile phase composition of gradient mixture of 3.9-3.6 mL/min $CO_2$, 0.1-0.4 mL/min methanol for 20 min. Resolutions of baccatin III, capalomannine, and 7-epi-10-deacetyltaxol were found to be low in this study. On-line coupled SFE/SFC process was applied to isolate paclitaxel from yew tree powder. As a consequence, paclitaxel with a purity of 95% was obtained with a recovery yield of 38%.

• KSBB Journal
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• v.16 no.1
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• pp.71-75
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• 2001

Acanthoside-D, contained in Acanthopanax chilsanensis is known as a ginseng-like substance. This work was focused to set up analytical and preparative conditions for Acanthoside-D purification. The ethanol extract from the powder of the trunk of Acanthopanax chilsanensis was partitioned with hexane. A $\mu$-Bondapak $C_{18}$ (3.9$\times$300 mm, $10\mu\textrm{m}$) column was used to separate Acanthoside-D from the trunk of Acanthopanax chilsanensis. From the experimental results, the mobile phase used for isolating Acanthoside-D from the extract was water/acetonitrile/methanol=80/14/6 %(v/v). The flow rate of mobile phase was 1.0 mL/min, and UV wavelength was fixed at 210 nm. Finally on a semi-preparative column (3.9$\times$ 300 mm, $15\mu\textrm{m}$, Lichrospher 100RP-18) with the same mobile phase composition, the allowable maximum injection volume increased to 250 $\mu\ell$