1,720,996 research outputs found
등적 수치적분을 이용한 외부 감마피폭의 실시간평가를 위한 이론적연구
No full text학위논문(박사) - 한국과학기술원 : 원자력공학과, 1995.2, [ xii, 147 p. ]An approximate method for estimating gamma external dose due to an arbitrary distribution of radioactive material has been developed. For the assessment of external gamma dose, the space over which radioactive material is distributed has been assumed to be composed of hexagonal cells. The evaluation of three-dimensional integration over the space is an extremely time-consuming task. Hence, a different approach has been used for the study, i.e., a equivalent-volume spherical approach in which a regular hexahedron is modeled as a equivalent-volume sphere to simplify the integration. For the justification of the current approach, two case studies have been performed: a comparison with a point source approximation and a comparison of external dose rate with the Monte Carlo integration. These comparisons show that the current approach gives reasonable results in a physical sense. Computing times of the developed and Monte Carlo integration method on VAX system have been compared as a function of the number of hexagonal cells. This comparison shows that CPU times for both methods are comparable in the region of small number of cells, but in the region of large number, Monte Carlo integration needs much more computing times. The proposed method is shown to have an accuracy equivalent to Monte Carlo method with an advantage of much shorter calculation time. Then, the method developed here evaluates early off-site consequences of a nuclear accident. An accident consequence assessment model has been integrated using Gaussian puff model which is used to obtain the distribution of radioactive material in the air and on the ground. For this work, the real meteorological data measured at Kori site for 10 years (1976 - 1985) have been statistically analyzed for obtaining site-specific conditions. The short-term external gamma exposures have been assessed for several site-specific meteorological conditions. The results show that the extent and the pattern of short-term externa...한국과학기술원 : 원자력공학과
산악지형에서의 원자력발전소 사고 시의 피폭 해석
No full text학위논문(석사) - 한국과학기술원 : 핵공학과, 1985.2, [ [v], 53 p. ]The Gaussian plume model is widely used to calculate the concentration of gaseous radioactive effluents in the atmosphere. This model assumes that the terrain is flat, so that the dispersion coefficients which are the most important parameters in this model must be compensated in complex terrain such as in Korea. In this study the compensation of vertical dispersion coefficient in two dimensional X-Z plane has been accomplished by comparing the Gaussian plume model with numerical model. The results show that the concentrations of radioactive effluents over complex terrain are more diluted than those expected over flat terrain.한국과학기술원 : 핵공학과
BEIR V 방법을 이용한 한국인의 방사선에 의한 암사망 예측
No full textThe lifetime fatal radiation-induced cancer for Korean has been estimated for both single and continuous radiation exposure using the BEIR V method. In case of single exposure, the major radiation-induced cancer type for young and old age is digestive and respiratory cancer, respectively. For the whole population of Korean, the major radiation-induced cancer type is digestive cancer. In case of 1mGy/yr continuous exposure from birth to death, the contribution of total radiation-induced cancer mortality to natural cancer mortality is about 3%
Morphology evolution of anatase TiO2 nanocrystals under a hydrothermal condition (pH=9.5) and their ultra-high photo-catalytic activity
No full textMorphology evolution of anatase TiO2 nanocrystals under a hydrothermal condition (pH = 9.5) was observed and a relationship between the morphology evolution and photo-catalytic activity was investigated. A titanium hydroxide nanogel was neutrally precipitated from a TiCl4 aqueous solution and then used as the precursor in the hydrothermal process. In the hydrothermal process, the nanogel was finally crystallized and grew to a capped bipyramidal nanocrystal which has faceted {101} pyramidal faces and are capped with rounded (001) faces, passing through an elongated structure with zigzag {101} faces. The final morphology was evolved via four growth stages in series: (i) formation and growth of anatase nuclei with consuming the nanogel, (ii) rapid growth along [0 0 1] direction by oriented attachments between (0 0 1) faces to produce an elongated structure with zigzag {101} pyramidal faces, (iii) flattening of zigzag {101} pyramidal faces by solution and precipitation, and (iv) rapid growth along [0 0 1] direction by solution and precipitation (Ostwald ripening). The photo-catalytic activity of anatase nanocrystals was closely related to the morphology evolution. Especially, the capped bipyramidal nanocrystals in the last growth stage showed an excellent photo-catalysis behavior: some of them were more than three times active than a commercial photo-catalyst (P25). The ultra-high photo-catalytic activity originated in the well-developed {101} surfaces, since the 4-coordinated Ti ions in the step edge of {101} face effectively adsorbed hydroxyl ions. Therefore, the particle morphology (surface property) was important as much as the particle diameter in TiO2 photo-catalysis. (c) 2005 Elsevier B.V. All rights reserved.The present work was financially supported in part by
the Research Institute of Industrial Science and Technology
(RIST) and in part by the Center for Nanostructured Materials
Technology (CNMT), Korea
Strength Degradation from Contact Fatigue in Self-toughened Glass-Ceramics
No full textWe investigated strength degradations from cyclic contact fatigue in self-toughened glass-ceramics. Hertzian indentation was used to induce cyclic contact load. Dynamic fatigue was also performed with changing stress rates form 0.01 to 10000 MPa/sec. After that, strength data and fracture origins were analysed. As the number of contact cycles increased or stressing rate decreased, severe strength degradation occurred by as much as 50% because of radial cracks developed form microcrack coalescenc
Material and Geometrical Design for High Reliability Bilayer
No full textCeramic/metal, ceramic/ceramic, and ceramic/polymer bilayers are prepared to find the best design for a reliable material. The transparent bilayer enables in situ observation of crack initiation. The elastic modulus of the substrate material in the bilayer is controlled from 2.35 GPa to 230 GPa by using different compositions of glass, metal, and polymer. The thickness of the ceramic coating layer is controlled from 120 ㎛ to 5.6 mm. The surface of tile coating material is abraded to control the strength and toughness. Classical cone cracks and transverse radial cracks are observed during Hertzian indentation. The crack initiations depend on not only material design parameters such as strength, toughness, and elastic modulus but also geometrical parameters such as coating thickness. Conditions for avoiding cracking are considered, in terms of the material and geometrical design parameters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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