• 설비공학논문집
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• 제7권3호
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• pp.366-381
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• 1995

A performance analysis of refrigeration system using the HFC-134a and scroll compressor is performed numerically. The refrigeration system mainly consists of various standard components such as heat exchanger, compressor, and expansion device. The model for heat exchanger performance is based on a tube-by-tube method which is analyzed separately by considering the cross-flow heat transfer with the outdoor air flow and pressure drop. Compressor is used the scroll-type compressor which has many merits such as high efficiency, low noise and vibration, and small in size. Short-tube is included as an expansion device. Vapour and liquid line are also considered for the performance analysis of refrigeration system. Using the modeling of various components of refrigeration system, a performance comparison of CFC-12 and HFC-134a is performed numerically for the various outdoor air temperature and various values of short-tube diameter. As the results of this study, the refrigeration system performance decreases as the outdoor air temperature increases. And the optimum short-tube diameter based on COP is 1.37mm for this system.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.67.1-67.1
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• 2012

Graphene has attracted much attention for future nanoelectronics due to its superior electrical properties. Owing to its extremely high carrier mobility and controllable carrier density, graphene is a promising material for practical applications, particularly as a channel layer of high-speed FET. Furthermore, the planar form of graphene is compatible with the conventional top-down CMOS fabrication processes and large-scale synthesis by chemical vapor deposition (CVD) process is also feasible. Despite these promising characteristics of graphene, much work must still be done in order to successfully develop graphene FET. One of the key issues is the process technique for gate dielectric formation because the channel mobility of graphene FET is drastically affected by the gate dielectric interface quality. Formation of high quality gate dielectric on graphene is still a challenging. Dirac voltage, the charge neutral point of the device, also strongly depends on gate dielectrics. Another performance killer in graphene FET is source/drain contact resistance, as the contact resistant between metal and graphene S/D is usually one order of magnitude higher than that between metal and silicon S/D. In this presentation, the key issues on graphene-based FET, including organic-inorganic hybrid gate dielectric formation, controlling of Dirac voltage, reduction of source/drain contact resistance, device structure optimization, graphene gate electrode for improvement of gate dielectric reliability, and CVD graphene transfer process issues are addressed.

• 플랜트 저널
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• 제8권2호
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• pp.52-58
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• 2012

Pipe means the connection of the tube in order to transfer fluid from one device to another device. The piping stress analysis is to analyze the structural stability considering the location and the features of piping support after completing the piping design, The allowable stresses comply with the requirements of the relevant standards by examining whether the support of the function and location of pipe or re-operation is confirmed. Allowable stresses are to make sure that the maximum stress should not exceed the allowable stress presented in the ASME B31.1 POWER PIPING code. ASME B31.1 POWER PIPING code ensures a smooth stress analysis can be performed during the initial pipe stress analysis as provided in the case of straight pipe to the horizontal distance between the supports. However, because there is no criteria set in the case of curved pipe, the optimum pipe supporting points were studied in this paper. As mentioned about the curved pipe, loads applied to the support of the position of 17% and 83% of the position relative to the elbow part have results similar to the load acting on the support of straight pipe.

• JSTS:Journal of Semiconductor Technology and Science
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• 제2권1호
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• pp.59-69
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• 2002

A semi-analytical model based on exact numerical analysis of the 2DEG channel in pseudo-morphic HEMT (PMHEMT) is presented. The exactness of the model stems from solving both Schrodinger's wave equation and Poisson's equation simultaneously and self-consistently. The analytical modeling of the device terminal characteristics in relation to the charge control model has allowed a best fit with the geometrical and structural parameters of the device. The numerically obtained data for the charge control of the channel are best fitted to analytical expressions which render the problem analytical. The obtained good agreement between experimental and modeled current/voltage characteristics and small signal parameters has confirmed the validity of the model over a wide range of biasing voltages. The model has been used to compare both the performance and characteristics of a PMHEMT with a competetive HEMT. The comparison between the two devices has been made in terms of 2DEG density, transfer characteristics, transconductance, gate capacitance and unity current gain cut-off frequency. The results show that PMHEMT outperforms the conventional HEMT in all considered parameters.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.843-845
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• 2009

A polymeric host for triplet emitters composed of N-alkylcarbazole and tetramethylbenzene units was successfully synthesized. Efficient energy transfer was observed between this polymeric host and green phosphorescent dyes. The device fabricated using 5 wt% green 1 in the polymeric host as the emitting layer showed the best performance. Thin films of this host-guest system, exhibiting clear stripe patterns could be prepared through the LITI process. The patterned films were then used to fabricate electrophosphorescent devices, which show performance characteristics similar to those of spin-coated devices. The new host material is a good candidate to be used in polymer-based full-color electrophosphorescent light-emitting displays.

• Transactions on Electrical and Electronic Materials
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• 제10권6호
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• pp.208-211
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• 2009

The authors have demonstrated the various characteristics of hybrid white organic light-emitting diodes (HWOLED) using fluorescent blue and phosphorescent red emitters. We also demonstrated that two devices showed different characteristics in accordance with thickness of the 4,4′-N,N′-dicarbazole-biphenyl (CBP) spacer (CS) inserted between the blue and the red emitting layer. It was found that the device with a CS thickness of 70 $\AA$ showed a current efficiency 2.5 times higher than that of the control device with a CS thickness of 30 $\AA$ by preventing the triplet Dexter energy transfer from the red to the blue emitting layer. The HWOLED with the CS thickness of 70 $\AA$ exhibited a maximum luminance of 24500 cd/$m^2$, a maximum current efficiency of 42.9 cd/A, a power efficiency of 37.5 lm/W, and Commission Internationale de I'Eclairage coordinates of (0.37, 0.42).

• 대한전자공학회논문지SD
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• 제44권7호통권361호
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• pp.1-8
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• 2007

고주파에서 동작하는 높은 출력전력과 dc-rf 변환효율을 가진 GaAs Gunn 다이오드에 대한 기본 연구로써, graded gap injector를 가진 planar 형태의 GaAs Gunn 다이오드를 제작하고 그 DC 특성을 살펴보았다. 제안된 에피 구조를 사용하여 GaAs Gunn 다이오드 소자를 설계, 제작하였으며 이동전자소자인 Gunn 다이오드의 DC 특성이 부성미분저항을 가짐을 확인하였다. 제작된 소자의 부성미분저항 특성을 다이오드의 cathode 반지름의 함수로 고찰하였으며, 이 과정을 통하여 계곡 간 전자이동 특성을 분석하였다.

• 대한임베디드공학회논문지
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• 제4권3호
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• pp.126-133
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• 2009

There are already many researches providing u-Healthcare service, but they have left problems to be improved. First of all, the transmission range between sensor nodes and the gateway are restricted. Hence, patients feel uncomfortable because of they need to possess or locate closed to a gateway all the time when they aggregates their medical data. Also, the existing systems have not considered life environment that is important to analyze patient's diseases. Moreover, a guardian need to located close to patient or possess a mobile device that monitors a patients' status in real time when they are in outdoor. In this research, we present multi-hop packet transfer algorithm and compilation of life environment which help improve the problem of the existing researches. Likewise, we designed and implemented a medical information database and a real-time web monitoring system that manage patients' personal history and monitor a patients' status in real time. In this paper, we design and implement the u-Healthcare system based on mobile environment and we present a result when we tested our u-Healthcare system in scenario environment.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 추계종합학술대회논문집
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• pp.149-152
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• 2000

스캐너는 문서, 사진, 필름 등을 스캔하여 디지털 데이터로 출력하는 장비이다. 이 중에서도 필름 스캐너는 네거티브/포지티브 필름을 스캔할 수 있는 스캐너이다. 본 논문에서는 스캐너를 구성하는 스텝모터 제어부, 이미지센서부, A/D converter 제어부 등을 설계하고 고속 신호처리를 위해 DSP를 사용한다. 또한 이런 주변기기와 DSP의 인터페이스 회로는 사용자가 임의의 논리회로를 프로그램 하여 내장할 수 있는 EPLD(Erasable Programmable Logic Device)를 이용한다. 스캐너를 제어하고 스캔된 데이터를 PC로 전송하기 위해 PC와의 인터페이스는 parallel 포트를 사용하며 35mm 필름을 스캔할 경우 9백만 화소 이상(수평 해상도 3835, 수직 해상도 2592)의 고해상도를 얻을 수 있도록 하드웨어를 설계한다.

• 한국광학회지
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• 제16권4호
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• pp.376-383
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• 2005

[ $Ti:LiNbO_3$ ] 채널 광도파로와 전기광학효과를 이용하여 설계된 집적광학 파장가변 편광모드 조절기를 설계 및 제작하고, 동작특성을 측정하였다. 소자는 $TE↔TM$ 모드변환기와 TE./TM 위상변환기로 구성되었으며, Jones 매트릭스를 이용하여 각각의 전달 매트릭스를 유도하였다. 위상변환기에 의한 파장 변환율을 전산 모사하였으며, 제작된 소자의 동작 특성들을 확인하였다. 폴래리미터와 Poincare 구 좌표계를 이용하여 편광 조절기의 동작 상태를 체계적으로 측정하였다.