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Designing and Performance Testings of Microdot Detectors
Hyosung Cho,Bongsoo Lee,Sin Kim 한국방사선학회 2007 한국방사선학회 논문지 Vol.1 No.3
We describe recent observations and measurements realized with microdot (MDOT) detectors having 50 mm, 100 mm, and 200 mm pitches for 3.7 keV X-rays. A gas gain of 3.1x103 has been measured with 50 mm pitch MDOT at potential difference much lower than those usually obtained with MSGCs. The defocusing effect caused by the existence of the readout lines passing below the insulator layer has been investigated from the drift voltage dependence of the count rate variation and the electric field simulation for all the detectors. Results concerning the spatial resolutions are presented with collimated X-ray beams.
Measurements of X-ray Imaging Performance of Granular Phosphors With Direct-Coupled CMOS Sensors
Cho, Min Kook,Kim, Ho Kyung,Graeve, Thorsten,Yun, Seung Man,Lim, Chang Hwy,Cho, Hyosung,Kim, Jung-Min IEEE 2008 IEEE transactions on nuclear science Vol.55 No.3
<P> For <TEX>${\hbox {Gd}}_{2}{\hbox {O}}_{2}{\hbox {S}}{:}{\hbox {Tb}}$</TEX> granular phosphor screens having a wide range of mass thicknesses, we have investigated the fundamental imaging performance in terms of modulation-transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE). As an optical photon readout device, a CMOS photodiode array with a pitch of 48 <TEX>$\mu{\hbox {m}}$</TEX> was used. Under the representative radiation quality, RQA 5, recommended by the IEC (International Electrotechnical Commission, Report 1267), the MTF was measured using a slanted-slit method to avoid aliasing and the NPS was determined by two-dimensional (2D) Fourier analysis of white images. The DQE was assessed from the measured MTF, NPS and the estimated photon fluence. Figure-of-merit (FOM) curves are presented to describe the tradeoff between the X-ray sensitivity and spatial resolution of screens as a function of mass thickness. This study will be useful for the selection guidance of <TEX>${\hbox {Gd}}_{2}{\hbox {O}}_{2}{\hbox {S}}{:}{\hbox {Tb}}$</TEX> phosphors for the relevant imaging tasks of digital radiography. </P>
Hyosung Cho,Bongsoo Lee,Sin Kim,Sungil Choi 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
We have developed a highly-integrated digital X-ray imaging sensor based upon a complementary-metal-oxide semiconductor (CMOS) array coupled with a columnar CsI(Tl) scintillator and an X-ray conversion fiberoptic plate for dental intraoral-imaging applications. The sensor consists of a commercially-available CMOS array with a 35 $\mu$m $\times$ 35 $\mu$m pixel size and a 24.1 mm $\times$ 31.6 mm active area, and a high-efficiency columnar CsI(Tl) scintillator of 90 $\mu$m in thickness directly deposited on a fiberoptic plate of a 6 $\mu$m in core size and 1.45 mm in thickness. In this paper, we describe the highly-integrated digital X-ray imaging sensor and evaluate its performance in terms of the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE), as indicators of image quality.
김효성(Hyosung Kim),신용태(Yongtae Shin),정인성(Insung Jung),조민수(Minsoo Cho),박재표(Jaepyo Park),강필용(Pilyong Kang) 한국정보과학회 1998 한국정보과학회 학술발표논문집 Vol.25 No.1A
동일한 데이터를 다수의 수신자들에게 전송해야 하는 어플리케이션들이 등장함에 따라 다중점(multipoint)그룹 통신 모형이 필요하게 되었다. 한 그룹의 프로세스들이 작업을 수행하기 위해서는 메시지들을 그룹의 참여자들에게 효율적으로 멀티캐스트할 수 있는 통신 메카니즘이 필요하다. 효율적인 멀티캐스트를 제공하기 위해서는 어플리케이션이 요구하는 사항을 상세히 분석한 다음, 그 어플리케이션이 요구하는 기능들만을 수행하는 경량화(lightweight)된 프로토콜을 설계해야 한다. 신뢰성있는 멀티캐스트 프로토콜이 제공할 수 있는 기능들은 주소 할당, 멤버쉽 관리, 신뢰성있는 전송, 그리고 서비스의 질(QoS)등이 있으며, 지금까지 제안된 멀티캐스트 프로토콜들은 재전송 역할자 위치, 가상 토폴로지, 어플리케이션 특성, 멤버쉽 관리, 그리고 프로토콜 계층에 따라 분류될 수 있다. 멀티캐스트 프로토콜을 설계하기 위해 고려해야 할 점들은 확장용이(scalability), 혼잡제어(congestion control), 오류회복(error recovery), 버퍼관리(buffer management), 그리고 주소할당(address allocation)등이다.
Choi, Hyosung,Cho, Heesook,Song, Suhee,Suh, Hongsuk,Park, Soojin,Kim, Jin Young Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.46
<P>We demonstrate the fabrication of a nanoporous titania (NP-TiO<SUB>2</SUB>) network structure by using a polystylene-<I>block</I>-poly(4-vinylpyridine) (PS-<I>b</I>-P4VP) diblock copolymer template and modifying the surface of NP-TiO<SUB>2</SUB> with ionic liquids (ILs), bmim-BF<SUB>4</SUB> and benmim-Cl. The effect of the molecular weight of PS-<I>b</I>-P4VP on the morphology of the NP-TiO<SUB>2</SUB> and IL-modified NP-TiO<SUB>2</SUB> are characterized by scanning electron microscopy and contact angle measurements. Subsequently, hybrid solar cells are fabricated using MEH-PPV and NP-TiO<SUB>2</SUB>, and the effect of IL layers and IL concentrations on device performances are evaluated under AM 1.5 G illumination. The devices containing bmim-BF<SUB>4</SUB> and benmim-Cl show drastically enhanced open circuit voltages (<I>V</I><SUB>oc</SUB>) of 1.05 V and 0.91 V, respectively, while the reference device without an IL layer exhibits a <I>V</I><SUB>oc</SUB> of 0.60 V. Significantly improved <I>V</I><SUB>oc</SUB> can be attributed to the change in interfacial energy levels by formation of ionic double layers at the TiO<SUB>2</SUB>/IL and at the IL/MEH-PPV interfaces. We also observed the trend that short circuit current decreased and <I>V</I><SUB>oc</SUB> increased with increasing IL concentration, which is ascribed to interruption of charge transfer from MEH-PPV to TiO<SUB>2</SUB> and the change in interfacial energy level by shifting the vacuum level, respectively.</P> <P>Graphic Abstract</P><P>The interfacial energy level of ionic double layers at the TiO<SUB>2</SUB>/MEH-PPV interface can change, resulting in remarkably improved open circuit voltages. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp01754j'> </P>
김효성(Hyosung Kim),신용태(Yongtae Shin),조민수(Minsoo Cho),곽재창(Jaechang Kwak) 한국정보과학회 1997 한국정보과학회 학술발표논문집 Vol.24 No.2Ⅲ
기존의 그룹통신은 네트워크나 프로세스에 중점적으로 연구가 진행되어 왔다. 그러나 본 논문에서는 유저의 관점에서 보다 유연하고 실질적인 그룹통신 환경을 제공하기 위해 네트워크와 유저 사이에서 이를 수행하는 관리 시스템을 제안한다. 그룹에서 회원관리를 하기 위한 그룹 서버의 프로토콜을 정의하고, 이와 연동해 그룹 서비스를 지원받는 유저의 프로토콜도 정의한다. 그리고 그룹통신을 이루는 프로세스와 인터넷에서의 그룹통신도 언급한다. 그룹에서 회원관리를 하기 위한 그룹 서버의 프로토콜을 정의하고, 이와 연동해 그룹 서비스를 지원 받는 유저의 프로토콜도 정의한다. 그리고 그룹통신을 이루는 프로세스와 인터넷에서의 그룹통신도 언급한다. 신뢰성잇는 그룹통신 관리시스템인 다모아는 그룹 관리 서비스, 회원 관리 서비스, 질의 서비스, 그룹 서비스, 그리고 응답 서비스로 구성된다, 이들 서비스를 수행하는데 필요한 프로토콜도 제안한다.
Je, Uikyu,Cho, Hyosung,Lee, Minsik,Oh, Jieun,Park, Yeonok,Hong, Daeki,Park, Cheulkyu,Cho, Heemoon,Choi, Sungil,Koo, Yangseo Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12
Recently, reducing radiation doses has become an issue of critical importance in the broader radiological community. As a possible technical approach, especially, in dental cone-beam computed tomography (CBCT), reconstruction from limited-angle view data (< 360A degrees) would enable fast scanning with reduced doses to the patient. In this study, we investigated and implemented an efficient reconstruction algorithm based on compressed-sensing (CS) theory for the scan geometry and performed systematic simulation works to investigate the image characteristics. We also performed experimental works by applying the algorithm to a commercially-available dental CBCT system to demonstrate its effectiveness for image reconstruction in incomplete data problems. We successfully reconstructed CBCT images with incomplete projections acquired at selected scan angles of 120, 150, 180, and 200A degrees with a fixed angle step of 1.2A degrees and evaluated the reconstruction quality quantitatively. Both simulation and experimental demonstrations of the CS-based reconstruction from limited-angle view data show that the algorithm can be applied directly to current dental CBCT systems for reducing the imaging doses and further improving the image quality.