• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.51-55
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• 2012

A few high-mass X-ray binaries-consisting of an OB star plus compact companion-have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) ${\gamma}$-rays. This paper focuses on the prominent ${\gamma}$-ray source, LS 5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical ($e{\approx}0.24$) orbit with its companion, assumed here to be an unmagnetized compact object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of ${\gamma}$-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of ${\gamma}$-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the ${\gamma}$-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite naturally fits the HESS light curve, thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE ${\gamma}$-ray emission in massive-star binaries.

• 폴리머
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• 제24권2호
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• pp.211-219
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• 2000

액정성을 가지는 플로렌계 발광고분자에 비버정성 플로렌계 발광고분자를 첨가한 블렌드를 제조하여 에너지전달 효과와 흡광 및 발광 이방성에 대하여 고찰하였다. 비액정성 고분자를 액정성 고분자에 0.5wt% 첨가하고 360nm로 여기한 결과, 420nm에서 관찰되었던 액정성 고분자의 발광피크는 거의 사라졌으며 대신 비액정성 고분자에 의한 480nm에서의 새로운 발광피크가 관찰되었다. 블렌드 시료의 480nm 발광은 비액정성 고분자가 2.0wt% 첨가되었을때 가장 강했으며, 발광강도는 블렌딩 이전의 각 고분자보다 13배 증자하였다. 블렌드내의 분자들을 마찰 폴리이미드 기판상에서 가열-냉각시켜 배향시키면 시료의 발광 이방성과 order parameter는 각각 2.0 및 0.25를 나타내었다. 시간 상관 단광자 계수법 (TCSPC)에 의해 고찰한 결과, 마찰 폴리이미드 기판상에서의 배향에 의해 두 발광고분자간의 에너지전달에 필요한 시간은 93 ps만큼 단축되며 에너지전달 효율은 9% 증가함을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2367-2370
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• 2014

"Cat's eye"-shaped $[^{57}Co]CoO@SiO_2$ core-shell nanostructure was prepared by the reverse microemulsion method combined with radioisotope technique to investigate a potential imaging agent for a single photon emission computed tomography (SPECT) in nuclear medicine. The core cobalt oxide nanorods were obtained by thermal decomposition of $Co-(oleate)_2$ precursor from radio isotope Co-57 containing cobalt chloride and sodium oleate. The $SiO_2$ coating on the surface of the core cobalt oxide nanorods was produced by hydrolysis and a condensation reaction of tetraethylorthosilicate (TEOS) in the water phase of the reverse microemulsion system. In vivo test, micro SPECT image was acquired with nude mice after 30 min of intravenous injection of $[^{57}Co]CoO@SiO_2$ core-shell nanostructure.

• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1904-1907
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• 2018

We designed a depth-encoding positron emission tomography (PET) detector by using a bottom and side readout method with a cross-arranged scintillator array. To evaluate the characteristics of the novel detector module, we used the DETECT2000 simulation tool to perform the optical photon transport in the crystal array. The detector module consists of an $M(column){\times}N(row)$ cross-arranged crystal array composed of M/3 sub-arrays consisting of $N{\times}3$ crystals. The second column of the sub-array is arranged perpendicular to the first and the third columns. The crystal is optically coupled to the crystals of the other columns; however, the surfaces between the crystals in the same column are treated as reflectors. A $6{\times}5$ crystal array consisting of two sub-arrays was considered for proof of concept. The two multi-pixel photon counter (MPPC) arrays are coupled to the bottom and one side of the crystal array, respectively. The x-y position is determined by the bottom MPPC array, and the side MPPC array gives depth information. All pixels in the x-y plane and the z direction were clearly distinguished.

• Current Applied Physics
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• 제18권11호
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• pp.1381-1387
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• 2018

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (${\Lambda}=700 nm$) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module. Apart from this, grating devices of smaller periodicity (${\Lambda}=280nm$) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3943-3948
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• 2022

Single-photon emission computed tomography is one of the reliable pin-by-pin verification techniques for spent-fuel assemblies. One of the challenges with this technique is to increase the total fuel assembly verification speed while maintaining high verification accuracy. The aim of the present study, therefore, was to develop an artificial intelligence (AI) algorithm-based tomographic image analysis technique for partial-defect verification of fuel assemblies. With the Monte Carlo (MC) simulation technique, a tomographic image dataset consisting of 511 fuel-rod patterns of a 3 × 3 fuel assembly was generated, and with these images, the VGG16, GoogLeNet, and ResNet models were trained. According to an evaluation of these models for different training dataset sizes, the ResNet model showed 100% pattern estimation accuracy. And, based on the different tomographic image qualities, all of the models showed almost 100% pattern estimation accuracy, even for low-quality images with unrecognizable fuel patterns. This study verified that an AI model can be effectively employed for accurate and fast partial-defect verification of fuel assemblies.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1527-1532
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• 2023

The noise reduction algorithm using the non-local means (NLM) approach is very efficient in nuclear medicine imaging. In this study, the applicability of the NLM noise reduction algorithm in single-photon emission computed tomography (SPECT) images with a brain phantom and the optimization of the NLM algorithm by changing the smoothing factors according to various reconstruction methods are investigated. Brain phantom images were reconstructed using filtered back projection (FBP) and ordered subset expectation maximization (OSEM). The smoothing factor of the NLM noise reduction algorithm determined the optimal coefficient of variation (COV) and contrast-to-noise ratio (CNR) results at a value of 0.020 in the FBP and OSEM reconstruction methods. We confirmed that the FBP- and OSEM-based SPECT images using the algorithm applied with the optimal smoothing factor improved the COV and CNR by 66.94% and 8.00% on average, respectively, compared to those of the original image. In conclusion, an optimized smoothing factor was derived from the NLM approach-based algorithm in brain SPECT images and may be applicable to various nuclear medicine imaging techniques in the future.

• 한국방사선학회논문지
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• 제12권7호
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• pp.929-934
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• 2018

영상의 질 향상과 물질 분석 등을 위해 엑스선을 카운팅하여 검출하기 위한 연구가 활발하다. 본 연구에서는 MPPC 어레이를 사용하여 엑스선 포톤 카운팅을 위한 검출기를 설계하였고, 시뮬레이션을 통해 검출기 특성을 평가하였다. GATE를 사용하여 엑스선과 섬광체와 반응한 위치 정보를 획득하였고, 이 정보를 DETECT2000의 빛 발생 위치로 사용하였다. 0.5 mm와 1 mm 두께의 GAGG 섬광체를 사용하였으며, $4{\times}4$ 어레이의 MPPC를 통해 발생된 빛을 획득하였다. 각 채널별로 획득한 빛의 신호를 통해 영상을 재구성하여 설계한 검출기의 분해능을 확인하였다. 0.5 mm와 1 mm 두께의 GAGG 섬광체에서 모두 2 lp/mm 이상의 영상을 획득하였다. 본 검출기를 엑스선 시스템에 사용할 경우 포톤 카운팅이 가능한 저비용의 시스템을 구축할 수 있을 것이다.

• Clinical and Experimental Pediatrics
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• 제52권7호
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• pp.804-810
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• 2009

목 적 : 영아연축은 이차성 전신간질중의 하나로 간질 병소를 발견하기 힘든 질환중의 하나이다. 이에 저자들은 $^{99m}Tc-ECD$ 추적자의 느린 점적 주사를 이용한 발작기 SPECT를 통하여 영아 연축 환아에서 간질 병소를 찾아보고자 하였다. 방 법 : 2005년 3월부터 2007년 2월까지 연세대학교 의과대학 소아과에 내원한 영아 연축 14명의 환아를 대상으로 첫 연축이 발생하는 시점에 $^{99m}Tc-ECD$ 를 2분에 걸쳐 천천히 같은 속도로 주입하였다. 발작간기와 발작기 간의 SPECT 의 차이를 비교하였으며 객관적인 비교를 위하여 SISCOM기법을 사용하였다. 또한 간질 병소를 발견할 수 있는 진단기법인 뇌파, 자기공명영상, 양전자단층촬영(PET) 등과 비교 분석하였다. 결 과 : 전체 14례의 추적자의 느린 점적 주사를 이용한 발작기 SPECT 중 10례에서 간질 병소의 혈류가 증가하였다. 비디오 뇌파와 발작기 SPECT에서 간질병소의 일치율은 Kappa=0.57, 95% confidence interval: 0.18-0.96로 높게 나왔다. 이 중 6례에서 발작기 SPECT와 비디오 뇌파에 근거하여 간질 수술을 시행하였으며 수술적 예후가 Engle class I으로 좋은 결과를 보였다. 결 론 : 추적자의 느린 점적 주사를 이용한 발작기 SPECT는 간질 병소를 찾기 어려운 영아 연축 환아에서 간질 병소를 찾아내는데 중요한 역할을 하는 것을 알 수 있었다. 그러나 보다 큰 규모의 전향적인 연구가 필요할 것으로 사료된다.

• Current Optics and Photonics
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• 제5권4호
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• pp.421-430
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• 2021

The multifocal multiphoton microscopy (MMM) enables high-speed imaging by the concurrent scanning and detection of multiple foci generated by lenslet array or diffractive optical element. The MMM system mainly suffers from crosstalk generated by scattered emission photons that form ghost images among adjacent channels. The ghost image which is a duplicate of the image acquired in sub-images significantly degrades overall image quality. To eliminate the ghost image, the photon reassignment method was established using maximum likelihood estimation. However, this post-processing method generally takes a longer time than image acquisition. In this regard, we propose a novel strategy for rapid noise reduction in the MMM system based upon Monte-Carlo (MC) simulation. Ballistic signal, scattering signal, and scattering noise of each channel are quantified in terms of photon distribution launched in tissue model based on MC simulation. From the analysis of photon distribution, we successfully eliminated the ghost images in the MMM sub-images. If the priori MC simulation under a certain optical condition is established at once, our simple, but robust post-processing technique will continuously provide the noise-reduced images, while significantly reducing the computational cost.