귀벌레는 자라서 오늘도 내 곁에 웅크리고

구현우 계간 서정시학 2022 서정시학 Vol.32 No.2

LED 조명용 반투명 유리 광확산판에 있어서 성형 및 냉각온도가 유백특성에 미치는 영향

구현우,임태영,김진호,이미재,황종희,신동욱,Ku, Hyun-Woo,Lim, Tae-Young,Hwang, Jonghee,Kim, Jin-Ho,Lee, Mi-Jai,Shin, Dong Wook 한국결정성장학회 2013 한국결정성장학회지 Vol.23 No.5

LED 조명등의 내구성 문제를 개선할 목적으로 광 확산판에 사용되는 폴리카보네이트 소재를 대체하기 위하여 반투명 유백유리를 제조하였다. 유백유리의 유백제로서 인산칼슘을 사용하였고, $1550^{\circ}C$ 전기로에서 2시간 용융하였다. 유백유리는 용융유리가 성형된 후 냉각 열처리 과정에서 상분리 및 유백입자의 성장에 의해 만들어진다. 따라서 성형 및 냉각온도를 상온, $850^{\circ}C$, $1100^{\circ}C$ 및 $1200^{\circ}C$ 로 변화시키면서 유백특성의 영향을 확인하였다. 결과적으로 가장 고온인 $1200^{\circ}C$에서 성형 및 냉각을 한 샘플에서 가장 양호한 특성을 갖는 유백유리가 얻어졌다. 이 유리는 82 % 이상의 높은 Haze 값과 10 % 미만의 낮은 평행광 투과도에 의해 직사광 투과에 의한 눈부심이 없이 LED 조명용 광확산판으로서 우수한 광특성을 나타내었다. 또한 열적특성으로서 $6.309{\times}10^{-6}/^{\circ}C$의 열팽창 계수와 $839^{\circ}C$의 연화점을 나타내었다. Translucent opal glass was fabricated in order to substitute polycarbonate diffuser of LED lighting for the purpose of improving the durability problem. Calcium phosphate was used for the opacifier of opal glass and melted at $1550^{\circ}C$ for 2 hrs in electric furnace. Because opal glass was made by phase separation and growth of opacifier grains during cooling procedure after forming of melted glass, we identified the effect of opaque properties by the change of forming and cooling temperature, as R.T. (room temperature), $850^{\circ}C$, $1100^{\circ}C$ and $1200^{\circ}C$. As the results, it had excellent optical properties for the diffuser of LED lighting in the fabricated sample of forming and cooling at $1200^{\circ}C$, with no dazzling from direct light by high haze value over 82 % and low parallel transmittance value under 10 %. For the thermal properties, it had expressed thermal expansion coefficient of $6.352{\times}10^{-6}/^{\circ}C$ and softening point of $839^{\circ}C$.

Whole-Body MRI in Children: Current Imaging Techniques and Clinical Applications

구현우 대한영상의학회 2015 Korean Journal of Radiology Vol.16 No.5

Whole-body magnetic resonance imaging (MRI) is increasingly used in children to evaluate the extent and distribution of various neoplastic and non-neoplastic diseases. Not using ionizing radiation is a major advantage of pediatric whole-body MRI. Coronal and sagittal short tau inversion recovery imaging is most commonly used as the fundamental whole-body MRI protocol. Diffusion-weighted imaging and Dixon-based imaging, which has been recently incorporated into whole-body MRI, are promising pulse sequences, particularly for pediatric oncology. Other pulse sequences may be added to increase diagnostic capability of whole-body MRI. Of importance, the overall whole-body MRI examination time should be less than 30–60 minutes in children, regardless of the imaging protocol. Established and potentially useful clinical applications of pediatric whole-body MRI are described.

미숙아의 태변전 증후군에 대한 초음파 유도하의 가스트로그라핀 관장법: 예비 결과

구현우,김기수,김애란,피수영,윤종현 대한영상의학회 2004 대한영상의학회지 Vol.50 No.4

정책분석의 세 가지 차원: 경제, 정치, 그리고 문화

구현우 한국지방정부학회 2019 한국지방정부학회 학술대회자료집 Vol.2019 No.11

Dual-Energy CT: New Horizon in Medical Imaging

구현우,구진모 대한영상의학회 2017 Korean Journal of Radiology Vol.18 No.4

Dual-energy CT has remained underutilized over the past decade probably due to a cumbersome workflow issue and current technical limitations. Clinical radiologists should be made aware of the potential clinical benefits of dual-energy CT over single-energy CT. To accomplish this aim, the basic principle, current acquisition methods with advantages and disadvantages, and various material-specific imaging methods as clinical applications of dual-energy CT should be addressed in detail. Current dual-energy CT acquisition methods include dual tubes with or without beam filtration, rapid voltage switching, dual-layer detector, split filter technique, and sequential scanning. Dual-energy material-specific imaging methods include virtual monoenergetic or monochromatic imaging, effective atomic number map, virtual non-contrast or unenhanced imaging, virtual non-calcium imaging, iodine map, inhaled xenon map, uric acid imaging, automatic bone removal, and lung vessels analysis. In this review, we focus on dual-energy CT imaging including related issues of radiation exposure to patients, scanning and post-processing options, and potential clinical benefits mainly to improve the understanding of clinical radiologists and thus, expand the clinical use of dual-energy CT; in addition, we briefly describe the current technical limitations of dual-energy CT and the current developments of photon-counting detector.

정책결정의 선택 논리: 합리성, 제약, 그리고 상징

구현우 서울대학교 한국행정연구소 2017 行政論叢 Vol.55 No.4

Policy has been determined for a long time by the logic of rationality in policy science. However it is true that there are many limitations. In particular, there have been many criticisms that it cannot adequately explain policy making. In this context, this study looks at constraints and symbols as well as rationality to analyze the selective logic of policy making better. First, it looked at the sources of constraints and the implications of choice within constraints. Sources of constraints were divided into rationality, power, and culture, and by doing so, explored why policy making depends on the logic of constraints, not the logic of rationality. The choice within constraints makes it easy to think of distorted policy making, though it does not necessarily mean that. It is the functional perspective of solving problems that cannot resolve the logic of rationality. Next, symbols are often overlooked in terms of traditional policy analysis, but have recently been emphasized in the context of social constructivism or cultural theory. The reason for focusing on symbolic elements such as culture in determining policy is because of the nature of politics and the specific aspect of the policy effect. The social perceptions of a policy target group or the symbol manipulations of political elites of a policy are highlighted as significant variables that go beyond material interests in this context of policy making. 오랫동안 정책학에서는 ‘합리성’의 논리에 따라 정책이 결정된다고 보았다. 신고전파 경제학에 강한 영향을 받았던 이러한 논리는 현상의 ‘미시적 기초(micro foundations)’를 정치하게 분석했다는 점에서는 그 의의를 찾을 수 있지만, 여러 가지 한계가 있는 것도 사실이다. 특히 현실의 정책결정을 제대로 설명할 수 없다는 실증적 한계는 뼈아픈 지적이 아닐 수 없다. 이러한 맥락에서 본 논문에서는 정책결정의 선택 논리를 보다 체계적으로 분석하기 위해 합리성뿐만 아니라, 제약과 상징에 대해서도 살펴보고 있다. 먼저 ‘제약’과 관련해서는 제약의 원천과 제약 하에서의 선택이 가지고 있는 함의에 대해 살펴보았다. 제약의 원천은 다시 제한된 합리성, 권력, 그리고 문화로 나누어 살펴보면서, 우리가 현실의 정책결정에서 합리성의 논리가 아닌 제약 하에서의 선택 논리에 좌우되는 이유를 보다 체계적으로 검토하였다. 이러한 제약 하에서의 선택은 현실의 정책결정을 왜곡하는 것으로 인식하기 쉬우나 반드시 그런 것은 아니며, 합리성의 논리로 해결하지 못하는 문제를 해결할 수 있는 ‘기능주의적’ 관점으로도 이해할 수 있다. 다음으로 ‘상징’과 관련해서는 전통적인 정책분석에서 흔히 간과하는 부분으로, ‘사회구성주의’나 ‘문화 이론’에 강한 영향을 받아 최근에 강조되고 있다. 우리가 정책을 결정함에 있어 상징과 같은 문화적 요소에 큰 영향을 받는 이유는 불확실하고 시차가 긴 정치의 본질적인 속성 때문이기도 하고, 정책효과의 다양한 양태가 정책대상집단의 인식에 영향을 주었기 때문이기도 하다. 상징과 같은 문화적 요소가 큰 영향을 받는 정책결정의 맥락 하에서는 정책대상집단에 대한 사회적 인식이 정책에 대한 대중의 반응에 결정적으로 중요하며, 정치엘리트들의 ‘상징조작’이 정책의 물질적 이해관계보다 우선시된다.

신천성 심장병 환자에서 다절편 전산화 단층촬영을 이용한 기도의 평가

구현우 한국소아심장연구회 2004 소아심장 Vol.8 No.1

Comparison of Chest Pain Protocols for Electrocardiography-Gated Dual-Source Cardiothoracic CT in Children and Adults: The Effect of Tube Current Saturation on Radiation Dose Reduction

구현우 대한영상의학회 2018 Korean Journal of Radiology Vol.19 No.1

Objective: To compare radiation doses between conventional and chest pain protocols using dual-source retrospectively electrocardiography (ECG)-gated cardiothoracic computed tomography (CT) in children and adults and assess the effect of tube current saturation on radiation dose reduction. Materials and Methods: This study included 104 patients (16.6 ± 7.7 years, range 5−48 years) that were divided into two groups: those with and those without tube current saturation. The estimated radiation doses of retrospectively ECG-gated spiral cardiothoracic CT were compared between conventional, uniphasic, and biphasic chest pain protocols acquired with the same imaging parameters in the same patients by using paired t tests. Dose reduction percentages, patient ages, volume CT dose index values, and tube current time products per rotation were compared between the two groups by using unpaired t tests. A p value < 0.05 was considered significant. Results: The volume CT dose index values of the biphasic chest pain protocol (10.8 ± 3.9 mGy) were significantly lower than those of the conventional protocol (12.2 ± 4.7 mGy, p < 0.001) and those of the uniphasic chest pain protocol (12.9 ± 4.9 mGy, p < 0.001). The dose-saving effect of biphasic chest pain protocol was significantly less with a saturated tube current (4.5 ± 10.2%) than with unsaturated tube current method (14.8 ± 11.5%, p < 0.001). In 76 patients using 100 kVp, patient age showed no significant differences between the groups with and without tube current saturation in all protocols (p > 0.05); the groups with tube current saturation showed significantly higher volume CT dose index values (p < 0.01) and tube current time product per rotation (p < 0.001) than the groups without tube current saturation in all protocols. Conclusion: The radiation dose of dual-source retrospectively ECG-gated spiral cardiothoracic CT can be reduced by approximately 15% by using the biphasic chest pain protocol instead of the conventional protocol in children and adults if radiation dose parameters are further optimized to avoid tube current saturation.

Calcium Phosphate 유백제 투입량에 따른 LED Diffuser용 유백유리의 특성

구현우,임태영,황종희,김진호,이미재,신동욱,Ku, Hyun-Woo,Lim, Tae-Young,Hwang, Jonghee,Kim, Jin-Ho,Lee, Mi-Jai,Shin, Dong Wook 한국세라믹학회 2013 한국세라믹학회지 Vol.50 No.1

We fabricated translucent opal glass to replace the polycarbonate diffuser in LED lighting systems in order to solve the durability problem. Batch materials of opal glass with a composition of calcium phosphate were created and melted at $1550^{\circ}C$, and the effect of opaqueness was identified by an addition of 1~7% calcium phosphate as an opacifier raw material. As a result, translucent opal glass was obtained by the melting of the mixed batch materials with a composition of more than 5% calcium phosphate glass at $1550^{\circ}C$ for 2 hrs, which had excellent optical properties for the diffuser of a LED lighting system with no dazzling from direct light by a high haze value exceeding 90% and a low parallel transmittance value of about 5%. For the thermal properties, the thermal expansion coefficient was found to be $5.6{\sim}5.9{\times}10^{-6}/^{\circ}C$ and the softening point was $874{\sim}884^{\circ}C$. In addition, good thermal properties such as good thermal shock resistance and feasibility for use with a general manufacturing process during the forming of glass tubes and bulbs were noted. Therefore, it is concluded that this translucent opal glass can be used as a glass diffuser material for LED lighting due to its high heat resistance and high durability as a replacement for a polycarbonate diffuser.