• 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.

• 천문학회보
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• 제45권1호
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• pp.34.1-34.1
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• 2020

The recent discovery of diffuse dwarf galaxies that are deficient in dark matter appears to challenge the current paradigm of structure formation in our Universe. We describe the numerical experiments to determine if the so-called dark matter deficient galaxies (DMDGs) could be produced when two gas-rich, dwarf-sized galaxies collide with a high relative velocity of ~ 300km/s. Using idealized high-resolution simulations with both mesh-based and particle-based gravito-hydrodynamics codes, we find that DMDGs can form as high-velocity galaxy collisions separate dark matter from the warm disk gas which subsequently is compressed by shock and tidal interaction to form stars. Then using a large simulated universe ILLUSTRISTNG, we discover a number of high-velocity galaxy collision events in which DMDGs are expected to form. However, we did not find evidence that these types of collisions actually produced DMDGs in the ILLUSTRISTNG100-1 run. We argue that the resolution of the numerical experiment is critical to realize the "collision-induced" DMDG formation scenario. Our results demonstrate one of many routes in which galaxies could form with unconventional dark matter fractions.

• 한국주조공학회지
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• 제17권4호
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• pp.402-410
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• 1997

Developing a salt core for squeeze casting process, two different salt cores(pure salt core and mixed salt core) were fabricated and investigated. Pure salt core was composed of 100% NaCl and mixed salt core was made by mixtures of NaCl with MgO(1%), $Na_2B_4O_7$(2%), and talc(1%) as a binder or a strengthening agent. Salt cores were compacted to various theoretical density, heat treated, and then squeeze-cast with molten Al alloy(AC8A). The compression strength of salt cores were measured and the squeeze-cast products were examined for shape retention, infiltration of molten metal into the cores, and microstructures. The shape of salt core compacted at above 75% of the theoretical density was maintained stably. The higher theoretical density of salt cores gave higher compression strength, and the compression strength of mixed salt core was higher than that of pure salt core. Namely at 90% theoretical density, the compression strength of mixed salt core was $6.3 kg/mm^2$, compared to $4.6 kgmm^2$ for pure salt core. At a squeeze casting pressure of $1000 kg/cm^2$, molten Al alloy was infiltrated into pure salt core of under 85% of the theoretical density. At squeeze casting pressure of $1000 kg/cm^2$, only mixed salt core above 90% of the theoretical density were valid, but the shape of the core was altered in the case of pure salt core at 90% of theoretical density. A key factor for developing a salt core for squeeze casting process was estimated as the ultimate compressive strength of salt core.

• 대한조선학회논문집
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• 제59권6호
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• pp.400-412
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• 2022

This paper provides the results of numerical and theoretical predictions of oil outflows from damaged single-hull and double-hull ships.Theoretical equations derived from the unsteady Bernoulli equation and a CFD method for multi-phase flow analysis were used to estimate the oil outflow rate from cargo tank. The predicted oil outflow rate from a single-hull cargo tank damaged due to grounding and collision accidents showed a good agreement with the available experimental results in both numerical and theoretical analyses. However, in the case of the double-hull conditions, the time variation of the amount of water and oil mixture inside the ballast tank predicted by the theoretical equation showed some different behavior from the numerical results. The reason was that the interaction of the oil flow with the water inflow in the ballast tank was not reflected in the theoretical equations. In the problems of the initial pressure condition in the cargo and ballast tanks, the oil outflow and water inflow were delayed at the pressure condition that the tanks were sealed. When the flow interaction between the oil and water in the ballast tank was less complicated, the theoretical and the numerical results showed a good agreement with each other.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 봄 학술발표회 논문집
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• pp.187-194
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• 1998

• 호남수학학술지
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• 제19권1호
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• pp.53-59
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• 1997

• 호남수학학술지
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• 제19권1호
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• pp.1-20
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• 1997

• 정보관리학회지
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• 제23권2호
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• pp.21-37
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• 2006

학문의 지식체계를 형성하는데 있어서 하나의 일련과정으로 밀접하게 상호연관된 이론개발 및 이론활용 연구가 뒷받침되어야 한다는 전제 하에, 본 연구는 문헌정보학 연구논문의 이론개발 및 이론활용 사례의 양적/질적 측면을 조사함으로써 문헌정보학의 이론적 기반을 분석하고자 하였다. 특히, 본 연구는 세부주제영역에 따른 이론개발 및 이론활용 연구의 특성에 주목함으로써 문헌정보학의 이론적 기반 형성에 기여한 세부주제영역을 보다 구체적으로 파악하고자 하였다. 이를 위해 1984년부터 2003년에 출판된 1,661편의 연구논문을 대상으로 내용분석을 실시하였다. 분석결과, 22개의 세부주제영역 중에서 정보이용탐색, 정보검색, 도서관경영, 학술커뮤니케이션 영역이 이론개발과 이론활용의 모든 측면에 가장 큰 기여를 한것으로 나타났다. 또한 주제영역별로 생산된 논문 수에 따른 이론적 연구의 비율을 살펴보았을 때, 계량정보학과 전문직 영역에 대한 연구가 매우 이론적인 특성을 보였다. 이 외에 각 세부주제영역별로 사용된 이론을 분석하였을 때, 일부 세부주제영역 간에 유사한 이론적 기반을 공유하고 있는 것으로 나타났다.

• 가정과삶의질연구
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• 제13권4호
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• pp.1-14
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• 1995

Various theoretical models have developed io both a family research area and family therapy field on he basis of several family theories and social theories in order to understand the family life and its function. These theoretical models have give rise to provide not only a framework for family therapy bt also opportunities for the development of family studies. Regardless of the devotion of these theoretical models to a family therapy however some family therapy professions have suggested the disvergence between these models and practice because the models tend to confuse therapists in their actual practices Other family therapists on the other hand have claimed the convergence between these models and practice. One of the reasons for the issues of convergence and disvergence in the family therapy study would be that various theoretical models have different sometimes contradicatable definitions and explanations for same concept. Therefore the purpose of this paper is to investigate the extent of similarities and differences among these theoretical models of practice in a way of examining family models to compare Olson's circumplex model to the Beavers systems model. Both models were based on the general systems theory. This paper consists of the explanation of Olson's circumplex model and Beavers systems model in general respectively. Then it will investigate similarities and differences between these two models in terms of the relationship between family functioning and family adaptability.

• Journal of Korean Biological Nursing Science
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• 제17권3호
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• pp.219-227
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• 2015

Purpose: This study was conducted to review physiological mechanisms of internet addiction and to construct a theoretical framework for cognitive behavioral therapy for internet addicts. Methods: We searched for relevant literature in the PubMed and RISS databases using the terms "internet addiction", "internet game addiction", "internet abuser", and "online game". Only English, full-text articles published from 2000 to 2015 were included in this review of physiological indicators of internet addiction. Finally, 12 articles were selected for review. Results: The theoretical framework developed based on the review proposes that excessive internet use itself may induce physiological stress responses with an increase of stress-related hormones and neurotransmitters. Prolonged abnormal responses of these physiological features produce negative structural and functional changes in the prefrontal cortex, which is mainly involved in cognitive and executive functions. These changes may result in decreased cognitive function. As a stressor, excessive internet use leads to transforming voluntary use into involuntary, habitual use and thus promotes the development of internet addiction. Conclusion: The proposed theoretical framework encompasses cognitive processes that may contribute to the effects of internet use-induced physiological stress on internet addiction. We believe that this framework has important implications for developing cognitive behavioral strategies for internet addicts.