• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.61-64
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• 2001

본 논문에서는 class간의 변별력을 증가시키기 위한 유용한 방법인 LDA(Linear Discriminant Analysis)를 사용하여 한국어 숫자음간의 변별력을 높여 연결숫자 인식성능을 높이고자 하였다. 한국어 숫자음은 모두 단음절이며 또한 혼동가능성이 높은 숫자쌍이 존재하여 이것이 전체 인식률을 저하시킨다. LDA를 사용한 경우 숫자열 오인식률이 $8\%$ 감소하였다. 그리고, 음성특징 벡터의 차수를 감소시키고 LDA 사용전 보다 약간의 인식률 증가를 보였다. 그러나, 선형적인 방법으로 분리가 불가능한 class들의 분포가 존재할 때는 LDA를 사용하여도 변별력 향상은 기대하기 어렵다. 이와 같은 분포의 class사이의 변별력을 증가시키기 위해 between-scatter covariance matrix를 구할 때 class 사이에 혼동가능성 정도를 나타내는 weighting factor를 적용하였으며, 그 결과 숫자열 오인식률이 LDA 사용전보다 $9.7\%$ 감소하였다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.113-119
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• 1998

Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

• The Journal of Korean Society for Radiation Therapy
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• v.6 no.1
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• pp.84-88
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• 1994

Proper evaluation about the penumbra is very important to improve the efficacy of radiation theraphy. There are two kinds of physical penumbra, geometric penumbra and transmission penumbra. In this study, we evaluated the variation of physical penumbra according to the varing enery level, changing the field size and depth. Physical penumbra width was decreased as the source size decreased, and as the SDD increased, but the consideration about the scatter radiation and mechanical stability is an important factor. For the two adjacent beams, upper collimator should be used and especially for Co-60 unit, it is efficient to use the extended collimator.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.1
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• pp.37-44
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• 2002

An echo signal in the active sonar using a high frequency is mainly formed of a specular reflection from the surface of an object along with several equivalent scatter inside, which are characterized by the spatial distribution of the highlights on the object. This thesis proposed a model in which the synthesized echo signal can be expressed as a distributed simulated target. The proposed model is obtained after composing a signal based on the movement of highlights relative to the aspect angle from the discontinuous point of an external hull with a strong reflection from a spheroid underwater target. Because the proposed algorithm includes a synthesis of the signals related to the highlight spacial distribution, it can be applied to all kinds of systems used at a short range, and similar results were obtained to the actual measured results of all reflected signals in previous literature referring to the irregular factor application of an envelope.

• Journal of radiological science and technology
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• v.16 no.2
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• pp.81-86
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• 1993

Proper evaluation about the penumbra is very important to improve the efficacy of radiation theraphy. There are two kinds of physical penumbra, geometric penumbra and transmission penumbra. In this study, we evaluated the variation of physical penumbra according to the varing energy level, changing the field size and depth. Physical penumbra width was decreased as the source size decreased, and as the SDD increased, but the consideration about the scatter radiation and mechanical stability is an important factor. For the two adjacent beams, upper collimator should be used and especially for Co-60 unit, it is efficient to use the extended collimator.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.183-188
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• 2012

Purpose: The concern of improving the quality of life and reducing side effects related to cancer treatment has been a subject of interest in recent years with advances in cancer treatment techniques and increasing survival time. This study is an analysis of differing scattered dose to the contralateral breast using common different treatment techniques. Materials and Methods: Eclipse 10.0 (Varian, USA) based $30^{\circ}$ EDW (Enhanced dynamic wedge) plan, $15^{\circ}$ wedge plan, $30^{\circ}$ wedge plan, Open beam plan, FiF (field in field) plan were established using CT image of breast phantom which in our hospital. Each treatment plan were designed to exposure 400 cGy using CL-6EX (VARIAN, USA) and we measured scattered dose at 1 cm, 3 cm, 5 cm, 9 cm away from medial side of the phantom at 1 cm depth using ionization chamber (FC 65G, IBA). We carried out measurement by separating effect of medial tangential field and lateral tangential field and analyze. Results: The evaluation of scattered dose to contralateral breast, $30^{\circ}$ EDW plan, $15^{\circ}$ wedge plan, $30^{\circ}$ wedge plan, Open beam plan, FIF plan showed 6.55%, 4.72%, 2.79%, 2.33%, 1.87% about prescription dose of each treatment plan. The result of scattered dose measurement by separating effect of medial tangential field and lateral tangential field results were 4.94%, 3.33%, 1.55%, 1.17%, 0.77% about prescription dose at medial tangential field and 1.61%, 1.40%, 1.24%, 1.16%, 1.10% at lateral tangential field along with measured distance. Conclusion: In our experiment, FiF treatment technique generates minimum of scattered dose to contralateral breast which come from mainly phantom scatter factor. Whereas $30^{\circ}$ wedge plan generates maximum of scattered doses to contralateral breast and 3.3% of them was scattered from gantry head. The description of treatment planning system showed a loss of precision for a relatively low scatter dose region. Scattered dose out of Treatment radiation field is relatively lower than prescription dose but, in decision of radiation therapy, it cannot be ignored that doses to contralateral breast are related with probability of secondary cancer.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.40-40
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• 2003

목적 : 현재 국내에서 사용중인 Co-60 원격치료용 방사선 조사장치의 경우 tissue air ratio(TAR)는 조사 표면에서 최대 선량을 가지는 back scatter factor(BSF)를 적용하여 구한 값을 사용하고 있는데, 실제로 Co-60 원격치료용 방사선 조사장치의 최대선량 깊이는 조사 표면이 아니라, 조사 표면에서 0.5cm 떨어진 거리에서 최대 선량을 나타내므로, BJR 25 에서 권장하는 값인 peak scatter factor(PSF)를 이용해 구한 값이 더 정확한 값으로 사료되기 때문에 이를 본 실험을 통해 검증하고자 하였다. 대상 및 방법 : 방사선 종양학과에서 치료용으로 사용하고 있는 Co-60 원격치료용 방사선 조사장치를 대상으로 하였다. BSF 는 Khan이 저술한 The Physics of Radiation Therapy의 부록에 제시된 값을 사용하였으며, PSF와 TAR를 구하기 위해 물 팬톰(water phantom), Farmer형 이온 챔버(ion chamber), 전기계(electrometer)를 사용하였다. PSF와 TAR를 구하기 위해서 몇 가지 측정을 하였다. 먼저, 공기 중에서 챔버를 SSD=80.5cm에 고정시킨 후, 방사선을 조사하여 선량을 측정하고, 깊이에 따른 선량을 알아보기 위해, 물 팬톰 내에 챔버를 SSD=80cm 고정시킨 후, 물을 서서히 채워가면서 5$\times$5cm, 10$\times$10cm, 15$\times$15cm, 20$\times$20cm, 30$\times$30cm의 field size에 대해서, 물의 깊이가 0.5cm-2cm 까지는 0.5cm 단위로 선량을 측정하고, 물의 깊이가 2cm-l4cm까지는 1cm단위로 선량을 측정하였다. 측정된 선량을 이용하여 PSF를 구하고 난 후, BJR 25에서 제시한 PSF와 비교를 하였고 TAR은 Khan이 제시한 변환식에 PSF를 대입하여 알아보았다. 기존의 TAR과 PSF를 이용해 구한 TAR을 측정하여 구한 TAR과 비교하였다. 결과 : BJR25에서 제시한 PSF와 본 실험에서 측정하여 얻은 PSF를 비교한 결과, field size가 5$\times$5cm, 10$\times$10cm, 15$\times$l5cm, 20$\times$20cm인 경우, 측정하여 얻은 PSF가 0.8%, 0.2%, 0.4%, 0.2%로 약간 높지만, 두 값은 매우 유사한 것으로 나타났다. 그리고, 기존의 BSF를 이용해 구한 TAR과 BJR 25에서 권고하는 PSF를 이용해 구한 TAR을 비교한 결과 field size 에 따라 약 1%-1.5% 정도로 BSF를 이용하여 구한 TAR보다 PSF를 이용하여 구한 TAR이 1.3% 정도 높게 나타났지만, 이것은 두 값의 절대적인 차이일 뿐, 실제로는 PSF를 이용하여 구한 TAR이 측정해서 구한 TAR과는 매우 유사한 값을 보여주고 있다. 결론 : 기존의 BSF를 이용해 구한 TAR과 PSF를 이용해 구한 TAR을 비교하였을 때, 약 1.3% 정도 높게 내고 있지만, 기존의 TAR보다는 PSF를 이용해 구한 TAR이 BJR 25와 잘 일치하고 있으므로 Co-60 원격치료용 방사선 조사장치를 사용할 경우 BSF보다는 PSF를 사용하는 것이 타당한 것으로 사료된다.

• The Journal of Korean Society for Radiation Therapy
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• v.8 no.1
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• pp.29-35
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• 1996

We are often faced with the clinical situations that is inevitably extended SSD for electron beam therapy due to anatomical restriction or applicator structure. But there are some difficulties in accurately predicting output and properties. In electron beam treatment , unlike photon beam the decrease in output for extended SSD does not follow inverse-square law accurately because of a loss of side scatter equilibrium, which is particularly significant for small cone size and low energies. The purpose of our study is to analyze the output in changing with the energy, cone size, air gap beyond the standard SSD and to compare inverse-square law factor derived from calculated effective SSD, mominal SSD with measured output factor. In addition, we have analyzed the change of PDD for several cones with different SSDs which range from 100cm to 120cm with 5cm step and with different energies(6MeV, 9MeV, 12MeV, 16MeV, 20MeV). In accordance with our study, an extended SSD produces a significant change in beam output, negligible change in depth dose which range from 100cm to 120cm SSDs. In order to deliver the more accurate dose to the neoplastic tissue, first of all we recommend inverse-square law using the table of effective SSDs with cone sizes and energies respectively or simply to create a table of extended SSD air gap correction factor. The second we need to have an insight into some change of dose distribution including PPD, penumbra caused by extended SSD for electron beam therapy.

• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.1
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• pp.33-42
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• 2014

Purpose: I-131 scan using High Energy (HE) collimator is generally used. While, Medium Energy (ME) collimator is not suggested to use in result of an excessive septal penetration effects, it is used to improve the sensitivities of count rate on lower dose of I-131. This research aims to evaluate I-131 SPECT/CT image quality using by HE and ME collimator and also find out the possibility of ME collimator clinical application. Materials and Methods: ME and HE collimator are substituted as Siemens symbia T16 SPECT/CT, using I-131 point source and NEMA NU-2 IQ phantom. Single Energy Window (SEW) and Triple Energy Windows (TEW) are applied for image acquisition and images with CTAC and Scatter correction application or not, applied different number of iteration and sub set are reconstructed by IR method, flash 3D. By analysis of acquired image, the comparison on sensitivities, contrast, noise and aspect ratio of two collimators are able to be evaluated. Results: ME Collimator is ahead of HE collimator in terms of sensitivity (ME collimator: 188.18 cps/MBq, HE collimator: 46.31 cps/MBq). For contrast, reconstruction image used by HE collimator with TEW, 16 subset 8 iteration applied CTAC is shown the highest contrast (TCQI=190.64). In same condition, ME collimator has lower contrast than HE collimator (TCQI=66.05). The lowest aspect ratio for ME collimator and HE collimator are 1.065 with SEW, CTAC (+) and 1.024 with TEW, CTAC (+) respectively. Conclusion: Selecting a proper collimator is important factor for image quality. This research finding tells that HE collimator, which is generally used for I-131 scan emitted high energy ${\gamma}$-ray is the most recommendable collimator for image quality. However, ME collimator is also applicable in condition of lower dose, lower sensitive if utilizing energy window, matrix size, IR parameter, CTAC and scatter correction appropriately.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.46.4-47
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• 2015

Carnegie Hubble Program II (hereafter CHP II) is a large Hubble Space Telescope (HST) observing campaign in the cycle 22 composed of a total of 184 orbits (132 primes + 52 parallels), which aims to measure H0 directly with an unprecedented accuracy. Unlike our previous efforts in CHP I which used Cepheids as a yardstick, CHP II takes the Population II (Pop II) distance indicators such as RR Lyraes and tip of the red giant branch stars (TRGBs) to set up a new calibration to Type Ia supernovae (SN Ia) distance. The Pop II distance scales have two immediate advantages over the classical Cepheid method: 1) The period-luminosity relation of the RR Lyrae has a scatter that is a factor of 2 smaller; 2) The RR Lyrae/TRGB distance scale can be applied to both elliptical and spiral galaxies. This will provide a great systematic benefit by ultimately allowing us to double the number of SN Ia distances based on geometry. By taking advantage of this Pop II route, we expect to measure H0 value to 3 % of error which will be the highest accuracy H0 measurement to date using the "Distance Ladder" method. In this talk I will present a brief background/overview on the CHP II, observations/data acquisition status, and ongoing research progress/preliminary results.