• Nuclear Engineering and Technology
• /
• 제54권3호
• /
• pp.991-996
• /
• 2022

Microstructures of monolithic high purity SiC and SiC with sintering additives after neutron irradiation to a fluence of 2.0-2.5 × 10²⁴ n/m² (E > 0.1 MeV) at 333-363 K and after post-irradiation annealing up to 1673 K were observed using a transmission electron microscopy. Results showed that no black spot defects or dislocation loops in SiC grains were found after the neutron irradiation for all of the specimens owing to the moderate fluence at low irradiation temperature. Thus, it is confirmed that these specimens were swelled mostly by the formation of point defects. Black spots and small dislocation loops were discovered only after the annealing process in PureBeta-SiC and CVD-SiC, where the swelling almost diminished. Anomalous-shaped YAG grains were found in SiC ceramics containing sintering additives. These grains contained dense black spots defects and might lose crystallinity after the neutron irradiation, while these defects may annihilate by recrystallization during annealing up to 1673 K. Amorphous grain boundary phase was also presented in this ceramic, and a large part of it was crystallized through post-irradiation annealing and could affect their recovery behavior.

• International Journal of Computer Science & Network Security
• /
• 제22권9호
• /
• pp.23-30
• /
• 2022

Glaucoma is a chronic neuropathy that affects the optic nerve which can lead to blindness. The detection and prediction of glaucoma become possible using deep neural networks. However, the detection performance relies on the availability of a large number of data. Therefore, we propose different frameworks, including a hybrid of a generative adversarial network and a convolutional neural network to automate and increase the performance of glaucoma detection. The proposed frameworks are evaluated using five public glaucoma datasets. The framework which uses a Deconvolutional Generative Adversarial Network (DCGAN) and a DenseNet pre-trained model achieves 99.6%, 99.08%, 99.4%, 98.69%, and 92.95% of classification accuracy on RIMONE, Drishti-GS, ACRIMA, ORIGA-light, and HRF datasets respectively. Based on the experimental results and evaluation, the proposed framework closely competes with the state-of-the-art methods using the five public glaucoma datasets without requiring any manually preprocessing step.

• Nuclear Engineering and Technology
• /
• 제56권5호
• /
• pp.1553-1561
• /
• 2024

Nondestructive radiography using cosmic ray muons has been used for decades to monitor nuclear reactor and spent nuclear fuel storage. Because nuclear fuel assemblies are highly dense and large, typical radiation probes such as x-rays cannot penetrate these target imaging objects. Although cosmic ray muons are highly penetrative for nuclear fuels as a result of their relatively high energy, the wide application of muon tomography is limited because of naturally low cosmic ray muon flux. This work presents a new image reconstruction algorithm to maximize the utility of cosmic ray muon in tomography applications. Muon momentum information is used to improve imaging resolution, as well as muon scattering angle. In this work, a new convolution was introduced known as M-value, which is a mathematical integration of two measured quantities: scattering angle and momentum. It captures the objects' quantity and density in a way that is easy to use with image reconstruction algorithms. The results demonstrate how to reconstruct images when muon momentum measurements are included in a typical muon scattering tomography algorithm. Using M-value improves muon tomography image resolution by replacing the scattering angle value without increasing computation costs. This new algorithm is projected to be a standard nondestructive radiography technique for spent nuclear fuel and nuclear material management.

• 대한지리학회지
• /
• 제41권2호
• /
• pp.150-167
• /
• 2006

이 연구는 미국 위스콘신 남부지방의 뢰스(loess)로 덮여있는 빙퇴석평야상의 소규모 저습지와 산록부에서 관찰되는 치밀차표층(dense subsurface horizons)의 형성원인과 형성과정을 설명하기 위한 것이다. 연구대상이 된 치밀차표층은 Bd 혹은 Bx층으로 명명될 수 있는 토양층이다. 일부 치밀차표층은 형태적으로 이쇄반층(fragipan, Bx)과 매우 유사한 특징을 보이지만, 아직까지 주변지역에서 이쇄반층의 존재가 보고된 바는 없다. 이 연구에서는 치밀차표층과 이쇄반층의 상대적인 분포의 차이를 지형기복과의 관계를 통해 관찰하였으며, 그 형성원인을 파악하기 위해 물리 화학적 분석과 더불어 토양구조의 현미경 관찰을 실시하였다. 그 결과 이쇄반층의 형성은 토양구조의 물리적인 숙성과정(physical ripening)과 그에 이은 콜로이드물질의 집적과정을 거치면서 형성된 것으로 결론을 내렸다. 치밀차표층에서 관찰되는 높은 밀도의 토양매질은 빙하가 물러나면서 형성된 소규모 빙하호수와 범람원에 퇴적된 뢰스물질들이 물리적인 숙성과정(physical ripening)을 거치면서 형성된 것으로 보이며, 그 결과 대규모의 주상구조(prismatic structure)가 형성되었다. 이후 지속적인 토양화과정을 거치면서 Si를 포함하는 콜로이드 물질의 집적에 의해 토양매질이 더욱 단단해지는 과정을 거치게 되면서 이쇄반층으로 발전하게 되었다. Si의 집적정도는 지형적인 특성과 물의 흐름에 의해 결정되게 된다. 물과 물질의 집적이 주로 나타나는 소규모의 저습지에서는 Si의 집적으로 인해 잘 발달된 이쇄반층(Bx)이 발달하게 된다. 반면, Si의 제거가 비교적 활발하게 이루어지는 산록부에서는 이쇄반층의 단계로 발전하지 못하고 치밀층(Bd)에 머물고 있는 것으로 판단된다. 이쇄반층이 만들어진 경우에는 그 상부에 불투수층이 형성되어, 물리적 숙성과정으로 형성된 주상구조의 상부가 서서히 파괴되는 현상을 보기에 된다. 이 경우에는 이쇄반층 상부에 용탈이쇄반층 (eluvial fragic horizon, Ex)이 나타나게 된다.

• 전기전자학회논문지
• /
• 제3권1호
• /
• pp.133-140
• /
• 1999

기존의 광통신 시스템을 DWDM에 사용할 경우, 인접 채널사이의 간격이 좁아 심한 간섭이 발생한다. FBG 필터를 사용하여 DWDM에서의 이러한 인접 채널간 간섭은 줄일 수 있다. 따라서, 본 논문에서는 균일한 경우, 가우시안 apodized 경우, 상승-코사인 apodized 경우의 세가지 굴절을 변화에 대한 반사 스팩트럼을 구하였다. 본 논문에서 얻어진 결과로 부터, 균일한 FBG는 적합하지 않고, 최대 굴절을 변화량 ${\sigma}$ 가 작을수록, 상승-코사인 apodized FBG 인 경우 변수 C 가 클수록, 가우시안 apodized FBG 인 경우 변수 G가클수록 DWDM용 협대역 필터에 적합함을 알 수 있었다. 또한, 상승-코사인 apodized FBG는 더 좁은 반사 스펙트럼 대역과 더 낮은 사이드로브를 갖기 때문에 가우시안 apodized FBG보다 더 우수한 특성을 갖음을 알 수 있었다.

• 천문학회보
• /
• 제43권1호
• /
• pp.43.1-43.1
• /
• 2018

Star formation in galaxies predominantly takes place in giant molecular clouds (GMCs). While it is widely believed that UV radiation feedback from young massive stars can destroy natal GMCs by exciting HII regions and driving their expansion, our understanding on how this actually occurs remains incomplete. To quantitatively assess the effect of UV radiation feedback on cloud disruption, we conduct a series of theoretical studies on the dynamics of HII regions and its role in controlling the star formation efficiency (SFE) and lifetime of GMCs in a wide range of star-forming environments. We first develop a semi-analytic model for the expansion of spherical dusty HII regions driven by the combination of gas and radiation pressures, finding that GMCs in normal disk galaxies are destroyed by gas-pressure driven expansion with SFE < 10%, while more dense and massive clouds with higher SFE are disrupted primarily by radiation pressure. Next, we turn to radiation hydrodynamic simulations of GMC dispersal to allow for self-consistent star formation as well as inhomogeneous density and velocity structures arising from supersonic turbulence. For this, we develop an efficient parallel algorithm for ray tracing method, which enables us to probe a range of cloud masses and sizes. Our parameter study shows that the net SFE, lifetime (measured in units of free-fall time), and the importance of radiation pressure (relative to photoionization) increase primarily with the initial surface density of the cloud. Unlike in the idealized spherical model, we find that the dominant mass loss mechanism is photoevaporation rather than dynamical ejection and that a significant fraction of radiation escapes through low optical-depth channels. We will discuss the astronomical.

• 한국분말재료학회지
• /
• 제21권6호
• /
• pp.467-472
• /
• 2014

RBSC (reaction-bonded silicon carbide) represents a family of composite ceramics processed by infiltrating with molten silicon into a skeleton of SiC particles and carbon in order to fabricate a fully dense body of silicon carbide. RBSC has been commercially used and widely studied for many years, because of its advantages, such as relatively low temperature for fabrication and easier to form components with near-net-shape and high relative density, compared with other sintering methods. In this study, RBSC was fabricated with different size of SiC in the raw material. Microstructure, thermal and mechanical properties were characterized with the reaction-sintered samples in order to examine the effect of SiC size on the thermal and mechanical properties of RBSC ceramics. Especially, phase volume fraction of each component phase, such as Si, SiC, and C, was evaluated by using an image analyzer. The relationship between microstructures and physical properties was also discussed.

• 수산해양기술연구
• /
• 제55권4호
• /
• pp.335-348
• /
• 2019

We found ten species of larvae belonging to the family Pleuronectidae as a result of analysis on ichthyoplankton collected monthly from the East Sea, Yellow Sea, Korea Strait and East China Sea between February 2016 and May 2018 using bongo net. The ten species of pleuronectid larvae were divided into three groups in morphology. Group A had three or four bars on the lateral side of the tail: Glyptocephalus stelleri, G. kitaharae, Pseudopleuronectes yokohamae, and Hippoglossoides dubius. Group B had a row of melanophores along the dorsal and ventral side of tail: Cleisthenes pinetorum, Eopsetta grigorjewi, Dexistes rikuzenius, and Platichthys bicoloratus. Group C had dense melanophores which are covering trunk and tail entirely except caudal peduncle: Platichthys cornutus and Platichthys japonicus. The three groups did not associate with previous molecular phylogenetic studies except for the G. stelleri and G. kitaharae of the group A.

• Nuclear Engineering and Technology
• /
• 제52권10호
• /
• pp.2370-2378
• /
• 2020

Building materials contribute significantly to the indoor radon and thoron levels. Therefore, parameters that influence the exhalation rates of radon and thoron from building material need to be analyzed closely. As a preliminary study, the effects of humidity on exhalation rates were measured using a system with an accumulation chamber and RAD7 detector for Korean brick, Korean soil, and Indonesian brick. Resulting doses to a person who resides in a room constructed from the building materials were assessed by UNSCEAR method for different air exchange rates. The measurements have revealed that Korean brick exhaled the highest radon and thoron while Indonesian brick exhaled the lowest thoron. Results showed that for a typical low dense material, radon and thoron exhalation rate will increase until reached its maximum at a certain value of humidity and will remain saturated above it. Analysis on concentration and effective dose showed that radon is strongly affected by air exchange rate (ACH). This is showed by about 66 times decrease of radon dose from 0.00 h^-1 to those of 0.50 h^-1 ACH and decrease by a factor of 2 from 0.50 h^-1 to those of 0.80 h^-1. In case of thoron, the ACH doesn't have significant effects on effective dose.

• Nuclear Engineering and Technology
• /
• 제50권2호
• /
• pp.223-228
• /
• 2018

AREVA NP (Courbevoie, Paris, France) is actively developing several enhanced accident-tolerant fuels cladding concepts ranging from near-term evolutionary (Cr-coated zirconium alloy cladding) to long-term revolutionary (SiC/SiC composite cladding) solutions, relying on its worldwide teams and partnerships, with programs and irradiations planned both in Europe and the United States. The most advanced and mature solution is a dense, adherent chromium coating on zirconium alloy cladding, which was initially developed along with the CEA and EDF in the French joint nuclear R&D program. The evaluation of the out-of-pile behavior of the Cr-coated cladding showed excellent results, suggesting enhanced reliability, enhanced operational flexibility, and improved economics in normal operating conditions. For example, because chromium is harder than zirconium, the Cr coating provides the cladding with a significantly improved wear resistance. Furthermore, Cr-coated samples exhibit extremely low corrosion kinetics in autoclave and prevents accelerated corrosion in harsh environments such as in water with 70 ppm Li leading to improved operational flexibility. Finally, AREVA NP has fabricated a physical vapor deposition prototype machine to coat full-length cladding tubes. This machine will be used for the manufacturing of full-length lead test rods in commercial reactors by 2019.