• 한국멀티미디어학회논문지
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• 제10권1호
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• pp.49-57
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• 2007

최근 무선통신 분야에서 가격, 소비전력과 칩 면적을 줄이기 위한 CMOS RF 집적화에 관한 연구가 수행되고 있다. 이동통신 단말기 수신단 구조 중 direct conversion 방식은 기존의 super-heterodyne 방식에 비해 IF단이 생략되어 수신단의 구조가 간단하고, RF 필터 등이 제거되어 one chip화가 가능하다는 장점을 갖는다. 그러나 direct conversion 구조는 발진 및 DC offset과 같은 문제점을 갖기 때문에 시스템 전체의 noise figure와 선형성 등을 고려하여 수신단용 필터와 VGA를 설계해야 한다. 본 논문에서는 direct conversion 구조의 이동통신 단말기용 프로그래머블 필터를 설계하였다. 제안된 필터 구조는 GSM, DECT, WCDMA와 같은 서로 다른 통신 방식에 적용할 수 있도록 차단주파수를 가변할 수 있고, RF단에서의 이득 변화에 대해 이득을 조절할 수 있도록 설계하였다. 설계된 프로그래머블 필터는 MOS 트랜지스터의 게이트 전압으로 차단주파수 부근에서 주파수를 조절할 수 있고, 제안된 구조는 필터 이득과 VGA를 이용하여 $27dB{\sim}72dB$까지 3dB 간격으로 이득을 가변할 수 있다.

• 한국산학기술학회논문지
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• 제10권12호
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• pp.3638-3644
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• 2009

본 논문에서는 새롭게 제안한 선형 캐스코드 전류모드 적분기를 기본으로 구성된 다중채널 CMOS 저전압 전류모드 필터를 설계하였다. 제안된 전류모드 적분기는 기존의 전류미러형 전류모드 적분기 비해서 높은 전류이득 및 단위이득 주파수 특성을 얻을 수 있다. 5차 체비셰프 함수로써 구성한 필터는 신호흐름선도(SFG)기법에 의하여 능동필터로 변환되었다. 1.8V-$0.18{\mu}m$ CMOS 공정파라미터를 사용한 HSPICE 시뮬레이션 결과, 설계된 필터는 0.51MHz에서 7.03MHz대역까지의 주파수 조정범위를 가지며 Bluetooth, DECT, WCDMA의 3채널의 기저대역에서 사용할 수 있음을 확인하였다.

• Journal of Radiation Protection and Research
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• 제43권1호
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• pp.1-9
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• 2018

Background: In this study, we investigate the image quality of virtual monochromatic images synthesized from dual-energy computed tomography (DECT) at voltages of 80/140 kV and 100/140 kV. Materials and Methods: Virtual monochromatic images of a phantom are synthesized from DECT scans from 40 to 70 keV in steps of 1 keV under the two combinations of tube voltages. The dose allocation of dual-energy (DE) scan is 50% for both low- and high-energy tubes. The virtual monochromatic images are compared to single-energy (SE) images at the same radiation dose. In the DE images, noise is reduced using the 100/140 kV scan at the optimal monochromatic energy. Virtual monochromatic images are reconstructed from 40 to 70 keV in 1-keV increments and analyzed using two quality indexes: noise and contrast-to-noise ratio (CNR). Results and Discussion: The DE scan mode with the 100/140 kV protocol achieved a better maximum CNR compared to the 80/140 kV protocol for various materials, except for adipose and brain. Image noise is reduced with the 100/140 kV protocol. The CNR values of DE with the 100/140 kV protocol is similar to or higher than that of SE at 120 kV at the same radiation dose. Furthermore, the maximum CNR with the 100/140 kV protocol is similar to or higher than that of the SE scan at 120 kV. Conclusion: It was found that the CNR achieved with the 100/140 kV protocol was better than that with the 80/140 kV protocol at optimal monochromatic energies. Virtual monochromatic imaging using the 100/140 kV protocol could be considered for application in breast, brain, lung, liver, and bone CT in accordance with the CNR results.

• 전자공학회논문지A
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• 제33A권2호
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• pp.40-49
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• 1996

In this paper, we studied channel assignment and handover schemes for the indoor microcell systems. For efficient frequency spectrum reuse we proposed the high quality reassignment (HQR) scheme. Proposed HQR scheme tries to keep the reuse distances small by monitoring C/I of channels being used. To assign a channel for a new or handove call, the scheme checks C/I of all available channels. Then HQR assigns the channel that has C/I near the threshold value, A_TH. The scheme also checks C/I of ongoing calls and continuously reassigns a new channel when needed. It attempts handover not only when C/I gets below a handover threshold value, HO_TH, but also when C/I becomes above a high quality reassignment threshold, H_TH. The performance of the proposed HQR scheme was analyzed by a computer simulation configuraed. The performance of the scheme was also analyzed for various threshold values selected and the results are presented in this paper. The results show that HQR scheme perfomrs better than the scheme adopted for DECT.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2002년도 추계학술발표논문집 (중)
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• pp.1027-1030
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• 2002

본 논문에서는 제 3세대 이동 통신 시스템에서 안전한 전자상거래의 구현을 위한 인증 및 지불 메커니즘을 제안한다. 제 3세대 이동 통신 환경에서는 GSM이나 DECT와 같은 제 2세대 이동 통신 시스템에서 사용되지 못했던 공개키 기반 구조를 도입하여 각 이동 단말기 사이에 공개키 암호 시스템을 이용한 통신이 가능하게 되었다. 이동 사용자는 TTP(Trusted Third Party)로부터 획득한 공개키 인증서를 사용하여 외부 도메인에서도 종단간의 통신을 할 수 있으며 디지털 콘텐츠를 제공하는 사이트에 접속하여 안전한 서비스를 제공받을 수 있다. 본 논문은 이동 통신 환경에 적합한 소액지불 기법을 기반으로 하여 이동 사용자와 VASP간의 상호 인증 및 지불에 관한 기법을 제안한다.

• 대한방사선치료학회지
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• 제29권1호
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• pp.77-84
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• 2017

목 적: 이중선원 듀얼에너지 CT(DS-DECT)의 가상 단색 영상을 이용해서 영상의 질 향상과 선량학적 영향에 대한 방사선치료계획 이용의 유용성을 평가하고자 한다. 대상 및 방법: DS-DECT를 이용하여 듀얼에너지(80/Sn 140 kVp)와 싱글에너지(120 kVp) 영상을 획득하였다. 영상 교정 팬텀 실험을 위해서 40-140 keV 범위로 단색 영상을 재구성했다. 선량 측정용 고체물등가팬텀 연구에서는 64, 69, 88, 105 keV 단색 영상을 선택했다. 스테인리스 스틸을 포함한 고체물등가팬텀에 $10{\times}10cm^2$ 조사야, SSD 100 cm, 10 MV 광자선, 100 MU 조사선량, 단일빔으로 치료계획을 수립하였다. 방사선량측면도 자료는 중심축에 위치한 4개의 지점에서 구했다. 싱글에너지 CT에서 획득한 다색 영상을 기준영상으로 하고, 가상 단색 영상의 선량학적 결과를 분석하였다. 결 과: 낮은 단색 에너지 수치에서 평균 감약이 증가했다. 7개의 물질 중에서 Teflon이 에너지 의존성이 가장 컸고, 10 keV 수치 상승으로 CT number가 평균 2.48 % 감소했다. 저밀도 공기에서는 단색 에너지에 대한 에너지 의존성이 없었다. Polystyrene, Acrylic은 70 keV 이상에서 안정한 CT number를 나타내었다. CT-ED 변환 곡선은 80 keV 단색 영상과 120 kVp 다색 영상이 비슷하였다. 단색 영상의 에너지가 증가할수록 금속의 식별 능력이 향상되었다. 줄무늬 인공음영은 105 keV 단색 영상에서 높은 감소를 보였지만, 여전히 남아 있었다. 다색 영상과 비교하여 각 영상에 따른 방사선치료계획의 선량학적 차이는 ${\pm}0.7%$ 미만이었다. 결 론: 듀얼에너지 영상의 획득은 싱글에너지에 비해 피폭선량을 감소시킬 수 있고, 가상 단색 영상은 CT number 보정에 유용하였다. 향상된 영상의 질은 인체의 기하구조 묘사와 전자 밀도 분포 형성에 도움이 될 것으로 사료된다.

• Archives of Reconstructive Microsurgery
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• 제3권1호
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• pp.54-63
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• 1994

Pulp and palm of the hand and heel of the sole are anatomically unique. Satisfactory reconstruction of these areas presents the plastic surgeon with many challenges and requires durable and sensible skin coverage, minimal donor morbidity and reliable operative procedure. We presents 7 clinical cases of sensate instep free flap transfer in this paper during the last 2 years. Three cases were soft tissue defects due to crushing and avulsion injury on the pulp of finger. 1 case was unstable scar and redundant flap after reconstruction of soft tissue dect of palm and 1 case was contracture of first web of hand. One case was a soft tissue defect due to avulsion injury on heel. Lastly, one case was chronic osteomyelitis with open wound on lateral malleolar area. Follow-up period ranged from 3 months to 2 years. Through the whole follow-up period, all flaps were viable and durable to persistant stress or weight bearing and were sensible enough to porotect the recocstructed area from injuries and maintain functions. In conclusions, the instep free flap should be considered as a valuable tool in reconstruction of hand and extremity requiring durability and sensation.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1342-1349
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• 2023

The planning accuracy of charged particle therapy (CPT) is subject to the accuracy of stopping power (SP) estimation. In this study, we propose a method of deriving a pseudo-triple-energy CT (pTECT) that can be achievable in the existing dual-energy CT (DECT) systems for better SP estimation. In order to remove the direct effect of errors in CT values, relative CT values according to three scanning voltage settings were used. CT values of each tissue substitute phantom were measured to show the non-linearity of the values thereby suggesting the absolute difference and ratio of CT values as parameters for SP estimation. Electron density, effective atomic number (EAN), mean excitation energy and SP were calculated based on these parameters. Two of conventional methods were implemented and compared to the proposed pTECT method in terms of residuals, absolute error and root-mean-square-error (RMSE). The proposed method outperformed the comparison methods in every evaluation metrics. Especially, the estimation error for EAN and mean excitation using pTECT were converging to zero. In this proof-of-concept study, we showed the feasibility of using three CT values for accurate SP estimation. Our suggested pTECT method indicates potential clinical utility of spectral CT imaging for CPT planning.

• 한국방사선학회논문지
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• 제17권7호
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• pp.1017-1023
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• 2023

The purpose of this study was to improve the accuracy of effective atomic number (EAN) and relative electron density (RED) using a polynomial-based calibration method using dual-energy CT images. A phantom composed of 11 tissue-equivalent materials was acquired with dual-energy CT to obtain low- and high-energy images. Using the acquired dual-energy images, the ratio of attenuation of low- and high-energy images for EAN was calibrated based on Stoichiometric, Quadratic, Cubic, Quartic polynomials. EAN and RED were extracted using each calibration method. As a result of the experiment, the average error of EAN using Cubic polynomial-based calibration was minimum. Even in the RED image extracted using EAN, the error of the Cubic polynomial-based RED was minimum. Cubic polynomial-based calibration contributes to improving the accuracy of EAN and RED, and would like to contribute to accurate diagnosis of lesions in CT examinations or quantification of various materials in the human body.

• Journal of Radiation Protection and Research
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• 제45권4호
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• pp.171-177
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• 2020

Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.