• 한국정보통신학회논문지
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• 제21권4호
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• pp.753-758
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• 2017

광선 슈팅 문제는 주어진 기하 객체들에 대해서 직선을 따라서 이동하는 광선이 처음으로 부딪히는 객체의 점을 찾는 문제이다. 광선은 보통 질의의 형태로 주어지기 때문에, 이 문제의 일반적인 해법은 다음과 같다. 먼저, 전처리 과정으로, 주어진 객체들에 대한 자료구조를 구축한다. 그 다음, 이 자료구조를 이용하여 각 질의에 대한 답을 빠르게 구한다. 본 논문에서는 x축 상에 놓인 수직 선분들 집합에 대한 광선 슈팅 문제를 고려한다. 본 논문에서는 입력으로 주어진 n개의 수직 선분들에 대해 볼록 레이어 트리라고 부르는 새로운 자료구조를 제시한다. 이것은 수직 선분들의 볼록 외피들의 레이어로 구성되는 이진 트리이다. 이 트리는 O(n log n) 시간과 O(n) 공간의 알고리즘으로 구축되며 구현이 용이하다. 또한 이 자료구조를 사용하여 각 질의를 O(log n) 시간에 수행하는 알고리즘을 제시한다.

• 대한방사선기술학회지:방사선기술과학
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• 제46권3호
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• pp.197-205
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• 2023

When taking X-rays, various auxiliary tools were used to fix a patient's exact shooting position and posture. In this study, we evaluated the usefulness of carbon fiber reinforced plastics(CFRP) 3K as a material of auxiliary tools by comparing poly methyl metha acrylate(PMMA), polycarbonate(PC), and CFRP 3K each of which has high radiolucency. X-ray radiolucencies were measured by stacking 1 mm panels of each material, and contrast to noise ratio(CNR) and signal to noise ratio(SNR) of images of each material were measured by comparing with None, which stands for images that are taken without any material. All three materials showed over 90% X-ray radiolucencies within 2 ㎜ thickness, and there was no significant difference. PC, PMMA and CFRP 3K had high CNR and SNR in order, and CFRP 3K showed the closest CNR and SNR to those of None. While taking X-rays, by using CFRP 3K material within 2 ㎜ thickness as a material of auxiliary tools, which are used to reduce re-shooting and X-ray exposure by fixing a patient's exact shooting position and posture and improve the quality of medical images, a high X-ray radiolucency of over 90% would be obtained, and the influence on the image could be minimized.

• 대한방사선기술학회지:방사선기술과학
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• 제40권1호
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• pp.71-78
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• 2017

디지털 방사선영상 시스템에서 산란선은 피검사체와 엑스선의 반응에 의해 발생하는 근원적인 현상이다. 방사선 투사영상은 일차선에 의해 형성되는 감쇠정보를 영상화 하므로 산란선은 투사영상에서 노이즈로써 작용한다. 본 연구에서는 다양한 검사조건에서 발생하는 산란선을 빔 저지체(beam stopper)를 이용하여 정량화하고 동시에 반 산란 격자의 효과를 확인하였다. 또한 산란선이 영상의 품질에 미치는 영향을 확인하기 위해 산란선에 의해 저하되는 대조도 대 잡음비를 측정하였다. 본 연구를 통해 산란선은 피검사체의 두께 및 공기층(air gap)에 지배적인 경향을 가짐을 확인하였다. 또한 산란선은 영상의 대조도를 현격히 저하시킴을 정량적으로 측정하였다. 산란선을 저감하기 위해 격자를 장착함으로써 상당량의 산란선을 저감할 수 있었으나 여전히 두꺼운 피검사체에 대해 많은 양의 산란선이 남아 있음을 확인하였다. 본 연구에서는 산란선을 정량화 하는 방법론을 제시하였으며, 향후 시스템의 최적화에 중요한 역할을 할 수 있을 것으로 기대된다.

• 전자공학회논문지A
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• 제32A권2호
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• pp.31-37
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• 1995

A ray-based approach is developed to calculate the scattering from inhomogeneous dielectric objects. This approach is a natural extension of the "shooting and bouncing ray(SBR)" technique developed earlier for calculating the radar cross section of cavity structures and complex targets. In this formulation, a dense grid of rays representing the incident field is shot toward the scatterer. The curved trajectory, amplitude, phase and polarization of the ray fields inside the inhomogeneous object are computed numerically based on the laws of geometrical optics. The contributions of the exting rays to the exterior scattered field are then calculated by using the equivalence principle in conjunction with " a ray-tube integration" scheme. The ray-based approach is applied for the effect of an arcjet plasma plume on satellite reflector performance and backscattering from inhomogeneous objects.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제25권1호
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• pp.23-34
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• 1997

Seismic tomography using the graph theoretical method of ray tracing is performed in two synthetic data sets with laterally varying velocity structures. The straight-ray tomography shows so poor results in imaging the laterally varying velocity structure that the ray-traced tomographic techniques should be used. Conventional ray tracing methods have serious drawbacks, i.e. problems of convergence and local minima, when they are applied to seismic tomography. The graph theretical method finds good approximated raypaths in rapidly varying media even in shadow zones, where shooting methods meet with convergence problems. The graph theoretical method ensures the globally minimal traveltime raypath while bending methods often cause local minima problems. Especially, the graph theoretical method is efficient in case that many sources and receivers exist, since it can find the traveltimes and corresponding raypaths to all receivers from a specific source at one time. Moreover, the algorithm of graph theoretical method is easily applicable to the ray tracing in anisotropic media, and even to the three dimensional case. Among the row-active inversion techniques, the conjugate gradient (CG) method is used because of fast convergence and high efficiency. The iterative sequence of the ray tracing by the graph theoretical method and the inversion by the CG method is an efficient and robust algorithm for seismic tomography in laterally varying velocity structures.

• 대한디지털의료영상학회논문지
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• 제9권2호
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• pp.5-9
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• 2007

As developing the medical treatment image portion with the change of these times, PACS, which is able to digitalize image portion data, has a lot of data-based image data. Applying this PACS, we would like to settle down RNSXI(real-name shooting X -ray of inspector) system. We interviewed with P ACS's operators of university hospitals which is using PACS in Seoul about the present conditions whether using of RNSXI or not. And we inquired the RNSXI equipments, applying PACS database, and Interface conditions undertook to do in our hospital. All university hospitals in Seoul are set up the P ACS system. But no hospital use the RNSXI. In our hospital, we can check inspector' name or initials who exposure x-ray with the PACS Viewer by looking over equipments(CR, DR, US, MG, MR, CT) and Interface of the DICOM Header data. However, some equipments like RF and Angio can not check inspector' name or initials. Under the Film/System environment, RNSXI system has been used frequently like that inspector's signature or initial added to a patient data. Though the digital medical treatment was developed, RNSXI system was declined. It is necessary to using RNSXI system in order to improving radiologists' rights, even if it is not under the application of the medical treatment image laws. If RNSXI system use, radiologists should specialize in their major and the Repeat rate should be reduced. In environment of PACS, RNSXI system can be used by linking both the equipments and the Interface with a production enterprise of P ACS. Therefore RNSXI system applying the P ACS datebase should settle down in our medical system for being provided lots of data.

• 전자공학회논문지B
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• 제33B권12호
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• pp.113-121
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• 1996

This paper presents a 37.5kVA (125kVp, 300mA) high frequency inverter type power supply for diagonostic X-ray generator with two HFHV (high-frequency high-voltage) isolating transformers. The output regulations, X-ray tuve voltage and tube current, are obtained by two high frequency inverters with the each other feedback PI controller and operating time switch for selecting shooting time and synchronizing two inverters. The operating modes and design consideration of the proposed power supply are given. Issues in the design of two HFHV isolating transformersfors high volage genrating and filament heating are discussed. Experimental results are presented to verify the performance of the designed power supply for varying load conditions. The proposed apparatus has several advnatages, e.g., the fast rising time of tube voltae, accuracy and reduced component size etc.

• 한국광학회:학술대회논문집
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• 한국광학회 1990년도 제5회 파동 및 레이저 학술발표회 5th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.49-53
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• 1990

Laser plasma was generated by a 1 GW iodine photodissociation laser(λ=1.315${\mu}{\textrm}{m}$, E-12.7J) whose output beam was focused on a molybdenum target surface. The experiment was conducted in the vacuum chamber under 10-5Torr and several tens of laser shooting were necessary for sufficient exposure to the PBS resist. A speciman was put directly on the resist and located at a distance of 3cm from the X-ray source. The replicas of a mesh, spider's tread, a red blood cell were obtained by PBS resist and were analyzed by Nomarski and SEM. Two main effects of limitation in resolution, source size and Fresnel diffraction, are mentioned and compared with the experimental result. In this experiment, a resolution better than 1000A could be obtained.

• 한국정보과학회논문지:시스템및이론
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• 제35권3호
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• pp.133-140
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• 2008

본 논문은 GPU상에서 작동되는 ray tracing을 위한 효과적인 k-D tree 탐색 알고리즘을 제안한다. 기존의 k-D tree를 위한 GPU 기반 탐색 알고리즘은 임의의 단말노드에서 교차되는 primitive를 찾지 못한 경우. root 노드 방향으로 bottom-up 탐색하여 부모 노드에서 bounding box 교차검사를 이용해 형제 노드의 기 방문 여부를 판단한다. 이러한 방법은 이미 방문한 부모 노드의 방문과 bounding box 교차검사를 중복적으로 수행한다. 본 논문에서 제안하는 알고리즘은 bottom-up 탐색을 수행 할 때 형제노드가 이전에 방문했는지를 확인할 수 있는 효율적인 방법을 제시함으로써 형제노드 및 부모로드의 방문을 생략하도록 하고, 또한 아직 방문하지 않은 노드에 대해서만 bounding box 교차검사를 수행함으로써 중복된 연산을 피한다. 결과적으로 본 논문의 실험은 기존 알고리즘 대비 제안하는 알고리즘이 약 30%의 성능 향상이 있음을 보여 준다.

• Design & Manufacturing
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• 제16권2호
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• pp.33-38
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• 2022

Currently, Korea is an aging society, and it is expected to enter a super-aging society in about 4 years. Accordingly, many X-ray technologies are being developed. In X-rays, 99% of X-rays are converted into heat energy and 1% into light energy (X-rays). 99% of the thermal energy raises the temperature of the anode and its surroundings, and the cooling system is an important factor as overheating can affect the deterioration of X-ray quality and shortened lifespan. There is a method of forced air cooling using natural convection. Therefore, in this study, when X-rays were taken 5 times, Flow analysis was performed on heat removal according to temperature rise and cooling time for the heat generated at the anode of the X-ray tube (input power 60kW, 75kW, 90kW). Based on one-shot, the most rapid temperature rise section increased by more than 57% to 0.03 seconds, A constant temperature rises from 0.03 seconds to 0.1 seconds, It is judged that the temperature rises by about 8.2% or more at one time. After one-shot cooling, the cooling drops sharply from about 60% to 0.03 seconds, It is judged that the temperature has cooled by more than 86% compared to the temperature before shooting. One-shot is cooled by more than 86% with cooling time after 0.1 seconds, As the input power of the anode increases, the cooling temperature gradually increases. Since the tungsten of the anode target inside the X-ray tube may be damaged by thermal shock caused by a rapid temperature rise, an improvement method for removing thermal energy is required when using a high-input power supply.