• Kyungpook Mathematical Journal
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• 제57권1호
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• pp.145-161
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• 2017

If a virtual knot diagram can be transformed to another virtual one by a finite sequence of crossing changes, Reidemeister moves and virtual moves then the two virtual knot diagrams are said to be homotopic. There are infinitely many homotopy classes of virtual knot diagrams. We give necessary conditions by using polynomial invariants of virtual knots for two virtual knots to be homotopic. For a sequence S of crossing changes, Reidemeister moves and virtual moves between two homotopic virtual knot diagrams, we give a lower bound for the number of crossing changes in S by using the affine index polynomial introduced in [13]. In [10], the first author gave the q-polynomial of a virtual knot diagram to find Reidemeister moves of virtually isotopic virtual knot diagrams. We find how to apply Reidemeister moves by using the q-polynomial to show homotopy of two virtual knot diagrams.

• Kyungpook Mathematical Journal
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• 제56권4호
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• pp.1247-1257
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• 2016

In this paper, we discuss the crossing change operation along exchangeable double curves of a surface-knot diagram. We show that under certain condition, a finite sequence of Roseman moves preserves the property of those exchangeable double curves. As an application for this result, we also define a numerical invariant for a set of surface-knots called du-exchangeable set.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1732-1750
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• 2010

Operation of KORAIL's level crossing is in charge of KORAIL. As taking over existing level crossing to KORAIL, they do not conduct risk assessments, so we do not know about any possibilities of inner risk. And present operation of safety of the level crossing is just regular checking of reaction and functions of safety equipments physically, we need to react to the changes of what's going on around of level crossing and incestigation of traffic flow and surrounding conditions more spontaneously. So, we have to prepare the strategies against accidents of level crossing cost-effectively based on regular risk assessments for sustainable safety improvements and overcome operational problems of present level crossing's safety. Here, we're going to investigate the level of safety level and present risk factors of the level crossing using risk assessments for accidents/error of the equipments to show operational strategies of level crossing based on risk assessments.

• Geomechanics and Engineering
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• 제20권2호
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• pp.103-112
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• 2020

The dynamic response of crossing tunnels under heavy-haul train loads is still not fully understood. In this study, based on the case of a high-speed tunnel underneath an existing heavy-haul railway tunnel, a model experiment was performed to research the dynamic response characteristics of crossing tunnels. It is found that the under-crossing changes the dynamic response of the existing tunnel and surrounding rock. The acceleration response of the existing tunnel enhances, and the dynamic stress of rock mass between crossing tunnels decreases after the excavation. Both tunneling and the excitation of heavy-haul train loads stretch the tunnel base, and the maximum tensile strain is 18.35 µε in this model test. Then, the measured results were validated by numerical simulation. Also, a parametric study was performed to discuss the influence of the relative position between crossing tunnels and the advanced support on the dynamic behavior of the existing tunnel, where an amplifying coefficient of tunnel vibration was introduced to describe the change in acceleration due to tunneling. These results reveal the dynamic amplifying phenomenon of the existing tunnel during the new tunnel construction, which can be referred in the dynamic design of crossing tunnels.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1756-1763
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• 2014

하천을 횡단하는 관로를 매설할 경우 하상변동으로 인해 관로가 드러나는 사고가 발생할 수 있으며 이를 방지하기 위해서는 안전한 매설경로를 분석할 필요가 있다. 본 연구에서는 금강을 횡단하는 도수관로의 안전한 매설구간 선정을 위해 2차원 수치모형을 이용하여 흐름해석 및 하상변동 분석을 수행하였다. 20년 빈도 홍수량을 적용한 모의 결과, 전반적으로 하상이 퇴적되는 것으로 나타났으나 교각의 영향을 받는 구간에서는 관로 매설 깊이 2 m 이상의 침식이 발생하는 것으로 나타났다. 극한 호우 사상에서도 교각 상류와 근접한 부근에서 관로매설 위치까지 침식이 발생하는 것으로 나타났다. 따라서 교각위치에서 상류 약 140 m 까지는 교각의 영향으로 하상침식이 매설된 관로에 영향을 미칠 것으로 예상된다. 상류 150 m 이후에 위치한 관로 횡단경로들은 하상 침식에 대해 상대적으로 안정적일 것으로 판단되어 안전을 고려하여 이를 도수관로 횡단경로의 최적구간으로 선정하였다.

• 천문학회보
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• 제40권1호
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• pp.85.2-86
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• 2015

The YORP effect is non-gravitational force that changes the spin-status of asteroid. So far this effect has been directly detected only from the Near-Earth asteroids (Taylor et al. 2007; Lowry et al. 2007, 2014; Breiter et al. 2011; Durech et al. 2008, 2012). Pravec at el. 2008 found the evidences for changing spin rate of small asteroids (3 - 15 km) by the YORP effect in the Main-Belt and Mars-crossing asteroids. The Mars-crossing asteroids (1.3 < q < 1.66 AU) are objects that cross orbit of the Mars. The Mars-crossing asteroids are regarded as one of the main sources for the Near-Earth asteroids. We expect that rotation of Mars-crossing asteroids would be influenced by the YORP effect. We try to search observational evidence of the YORP effect for the Mars-crossing asteroid. Our target 2078 Nanking is a population of the Mars-crossing asteroid. First light-curve of 2078 Nanking was obtained from Mohamed et al. 1994, and Warner et al. 2015 recently published new observational data. We observed this asteroid on 26th Nov. 2014 and 17th Jan. 2015 using SOAO (Sobaeksan Optical Astronomy Observatory) 0.61 m telescope with 4K CCD. Using light-curve inversion method (Kaasalainen & Torppa 2001; Kaasalainen et al. 2001), we try to determine the pole orientation and shape model of this asteroid based on the combination of our light-curve and literature photometric data. Knowing spin parameters, such as rotational period and spin axis, are essential for studying the YORP effect. In this presentation, we provide some preliminary results of our recent study: light-curve and processing of shape modeling of 2078 Nanking. We plan to find observational clue for the YORP effect on the Mars-crossing asteroids.

• Kyungpook Mathematical Journal
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• 제57권2호
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• pp.331-360
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• 2017

Unknotting numbers for torus knots and links are well known. In this paper, we present a new approach to determine the position of unknotting number crossing changes in a toric braid such that the closure of the resultant braid is equivalent to the trivial knot or link. Further we give unknotting numbers of more than 600 knots.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.1115-1118
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• 2000

In order to understand information of geographic information systems(GIS) exactly and easily, visualization technique becomes important. In this paper, we consider car-traffic which is one of the information accompanying with a map. Then, a visual simulation method is proposed for car-traffic flow at crossing with the cell-automaton and the ray tracing method. We simulate the various situations and discuss about changes of traffic.

• 한국연안방재학회지
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• 제4권3호
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• pp.119-131
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• 2017

Global warming under the influence of climate change and its direct impact on glacial and sea level are known issue. However, there is a lack of research on an indirect impact of climate change such as coastal structure design which is mainly based on a frequency analysis of water level under the stationary assumption, meaning that maximum sea level will not vary significantly over time. In general, stationary assumption does not hold and may not be valid under a changing climate. Therefore, this study aims to develop a novel approach to explore possible distributional changes in annual maximum sea levels (AMSLs) and provide the estimate of design water level for coastal structures using a multiple non-crossing quantile regression based nonstationary frequency analysis within a Bayesian framework. In this study, 20 tide gauge stations, where more than 30 years of hourly records are available, are considered. First, the possible distributional changes in the AMSLs are explored, focusing on the change in the scale and location parameter of the probability distributions. The most of the AMSLs are found to be upward-convergent/divergent pattern in the distribution, and the significance test on distributional changes is then performed. In this study, we confirm that a stationary assumption under the current climate characteristic may lead to underestimation of the design sea level, which results in increase in the failure risk in coastal structures. A detailed discussion on the role of the distribution changes for design water level is provided.

• 한국전문물리치료학회지
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• 제15권4호
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• pp.27-33
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• 2008

The purpose of this study was to investigate the changes of the center of pressure (COP) trajectory in healthy elderly subjects while crossing an obstacle before and after participation in Tai Chi training. Forty healthy elderly subjects participated either in a 12-week intervention of Tai Chi training or in a health education program. The participants were divided into two groups (the experimental group and the control group). Subsequently, the participants were pre- and post-tested on crossing over an obstacle from a quiet stance. Participants in the experimental group received Tai Chi training that emphasized the smooth integration of trunk rotation, a shift in weight bearing from bilateral to unilateral support and coordination and a gradual narrowing of the lower-extremity stance three times weekly. The participants in the control group attended a health education program one hour weekly and heard lectures about general information to promote health. Performance was assessed by recording the changes in the displacement of the COP in the anteroposterior (A-P) and mediolateral (M-L) directions using a force platform. Participants in the Tai Chi group significantly increased the A-P and M-L displacement of the COP after Tai Chi training (p<.05). No significant differences in the A-P and the M-L displacement of the COP between pre-testing and post-testing in the control group were found. This study has shown that participation in Tai Chi exercise increased the magnitude of the A-P and M-L displacement of the COP, thereby improving the ability of healthy elderly participation to generate momentum to initiate gait. These findings support the use of Tai Chi training as an effective fall-prevention program for the elderly.