• Wind and Structures
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• 제26권3호
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• pp.115-128
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• 2018

Appropriate modeling of a tornado-like vortex is a prerequisite when studying the near-ground wind characteristics of a tornado and tornado-induced wind loads on structures. Both Ward- and ISU-type tornado simulators employ guide vanes to induce angular momentum to converge flow in order to generate tornado-like vortices. But in the Ward-type simulator, the guide vanes are mounted near the ground while in the ISU-type they are located at a high position to allow vertical circulation of flow that creates a rotating downdraft to generate a tornado-like vortex. In this study, numerical simulations were performed to reproduce tornado-like vortices using both Ward-type and ISU-type tornado simulators, from which the effects of rotating downdraft on the vortex characteristics were clarified. Particular attention was devoted to the wander of tornado-like vortices, and their dependences on swirl ratio and fetch length were investigated. The present study showed that the dynamic vortex structure depends significantly on the vortex-generating mechanism, although the time-averaged structure remains similar. This feature should be taken into consideration when tornado-like-vortex simulators are utilized to investigate tornado-induced wind forces on structures.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.136-142
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• 2008

The influence of different grids on numerical prediction of subsonic compressor performance and stall was investigated. Two types of grids were examined, structured H type grid and structured O-H type grid. Evaluations were conducted by comparing the numerical results with experimental results obtained from a low-speed single-stage rig test for a new concept compressor, called diffuser passage compressor, aiming at improving tip clearance sensitivity. At low mass flow operating conditions, the numerical calculation with O-H type grid showed that the lowest mass flow operating point for which the calculation was able to converge was almost the same as the lowest steady mass flow obtained from the rig test. On the other hand, the numerical calculation with structured H type grid diverged at higher mass flow operating point. It was found that this difference was attributed to the effect of double-valuedness of H type grid that existed at leading edge on the boundary layer development on the blade surface.

• Journal of Korean Neurosurgical Society
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• 제62권3호
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• pp.313-320
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• 2019

Brain tumors are the second most common type of structural brain lesion that causes chronic epilepsy. Patients with low-grade brain tumors often experience chronic drug-resistant epilepsy starting in childhood, which led to the concept of long-term epilepsy-associated tumors (LEATs). Dysembryoplastic neuroepithelial tumor and ganglioglioma are representative LEATs and are characterized by young age of onset, frequent temporal lobe location, benign tumor biology, and chronic epilepsy. Although highly relevant in clinical epileptology, the concept of LEATs has been criticized in the neuro-oncology field. Recent genomic and molecular studies have challenged traditional views on LEATs and low-grade gliomas. Molecular studies have revealed that low-grade gliomas can largely be divided into three groups : LEATs, pediatric-type diffuse low-grade glioma (DLGG; astrocytoma and oligodendroglioma), and adult-type DLGG. There is substantial overlap between conventional LEATs and pediatric-type DLGG in regard to clinical features, histology, and molecular characteristics. LEATs and pediatric-type DLGG are characterized by mutations in BRAF, FGFR1, and MYB/MYBL1, which converge on the RAS-RAF-MAPK pathway. Gene (mutation)-centered classification of epilepsy-associated tumors could provide new insight into these heterogeneous and diverse neoplasms and may lead to novel molecular targeted therapies for epilepsy in the near future.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2002년도 춘계 학술발표회 논문집
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• pp.55-60
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• 2002

We present an extension of the Wong-Zakai type approximation theorem for a multiple stochastic integral. Using a piecewise linear approximation $W^{(n)}$ of a Wiener process W, we prove that the multiple integral processes {${\int}_{0}^{t}{\cdots}{\int}_{0}^{t}f(t_{1},{\cdots},t_{m})W^{(n)}(t_{1}){\cdots}W^{(n)}(t_{m}),t{\in}[0,T]$} where f is a given symmetric function in the space $C([0,T]^{m})$, converge to the multiple Stratonovich integral of f in the uniform $L^{2}$-sense.

• Journal of applied mathematics & informatics
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• 제36권1_2호
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• pp.135-154
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• 2018

In this paper, an almost second order overlapping Schwarz method for singularly perturbed third order convection-diffusion type problem is constructed. The method splits the original domain into two overlapping subdomains. A hybrid difference scheme is proposed in which on the boundary layer region we use the combination of classical finite difference scheme and central finite difference scheme on a uniform mesh while on the non-layer region we use the midpoint difference scheme on a uniform mesh. It is shown that the numerical approximations which converge in the maximum norm to the exact solution. We proved that, when appropriate subdomains are used, the method produces convergence of second order. Furthermore, it is shown that, two iterations are sufficient to achieve the expected accuracy. Numerical examples are presented to support the theoretical results. The main advantages of this method used with the proposed scheme are it reduce iteration counts very much and easily identifies in which iteration the Schwarz iterate terminates.

• 한국분무공학회지
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• 제22권3호
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• pp.116-121
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• 2017

Pre-combustion chamber type indirect diesel engines have different combustion characteristics compared with those of common rail direct injection engine. The CONVERGE, specific engine CFD program, was used to simulate hollow cone spray model and combustion. The air-fuel mixture flow propagating from pre-combustion chamber to cylinder was concentrated at top half and center of the pre-combustion chamber throat. Stronger mixture flow was formed at smaller and longer throat cases. As a result, thermal efficiency and fuel consumption were improved for modified throat shape and the soot emission was also reduced.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1234-1239
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• 1990

In this paper, we propose a new type of decentralized learning automata for the control finite state Markov chains with unknown transition probabilities and rewards. In our scheme a .betha.-type learning automaton is associated with each state in which two or more actions(desisions) are available. In this decentralized learning automata system, each learning automaton operates, requiring only local information, to improve its performance under local environment. From simulation results, it is shown that the decentralized learning automata will converge to the optimal policy that produces the most highly total expected reward with discounting in all initiall states.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권2호
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• pp.254-257
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• 2004

Both ground and space telescopes are being built larger and larger. Accordingly, the secondary mirrors become larger which are convex mostly on the surface form. Testing convex mirrors becomes more difficult and delicate than testing concave mirrors in optics, because additional optical components are needed to make the reflected rays converge. Hindle type tests are frequently used for measuring the surface deforms of convex mirrors, which employs a meniscus lens to reverse the diverted rays from the mirrors. In case of testing large convex mirrors by using Hindle type tests, attention would be needed as larger meniscus lens is required. A method of modified Hindle test has been studied and the characteristics are analyzed. In this paper, current method of testing convex mirrors is presented, and a new method is discussed.

• 보건행정학회지
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• 제30권3호
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• pp.409-417
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• 2020

Background: It is well known that the distribution of therapeutic materials is very complex. However, it is not easy to demonstrate the concrete problems caused by distribution channels empirically. The purpose of this study was to investigate the differences in the price of therapeutic materials according to the type of purchasing agency and the way in which medical institutions purchase therapeutic materials. Methods: This study compared the claimed prices and the maximum allowable prices for the items of therapeutic material used for general spinal surgery. Results: Ilsan Hospital, which purchased directly without a purchasing agent, had the lowest claimed prices, followed by a large professional purchasing agency, a foundation-related purchasing agency, and a general purchasing agency. In addition, the difference between the claimed prices and the maximum allowable prices according to the purchase type was larger in the expensive treatment materials, and in the case of the lower price treatment materials, it tended to converge to the maximum allowable prices. Conclusion: National health insurance spending for therapeutic materials are to be affected by the distribution channels of them. We proposed several ideas to rationalize the expenditure such as classification of therapeutic materials on the basis of price or other criteria.

• 한국경영과학회지
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• 제28권4호
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• pp.145-153
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• 2003

In this Paper, we examine the limiting distributional behaviour of extreme values of mixed Erlang random variables. We show that, in the finite mixture of Erlang distributions, the component distribution with an asymptotically dominant tail has a critical effect on the asymptotic extreme behavior of the mixture distribution and it converges to the Gumbel extreme-value distribution. Normalizing constants are also established. We apply this result to characterize the asymptotic distribution of maxima of sojourn times in M/M/s queuing system. We also show that Erlang mixtures with continuous mixing may converge to the Gumbel or Type II extreme-value distribution depending on their mixing distributions, considering two special cases of uniform mixing and exponential mixing.