• Journal of the Korean Geographical Society
• /
• v.40 no.5 s.110
• /
• pp.514-532
• /
• 2005

The purpose of this study is to critically examine conventional spatial measures of individual accessibility, which are based on the notion of spatial proximity, the single reference location, and the unlinked travel model. Using space-time accessibility measures with the travel-activity diary data set of Portland Metro, US, three expectations from spatial measures on spatial patterns of individual accessibility were empirically examined: (1) does individual accessibility decrease with an increase of distance from the CBD?; (2) does the spatial pattern of accessibility resemble that of urban opportunity density pattern?; and (3) are spatial patterns of individual accessibility of different socio- demographic population groups basically similar as people in the same area share the same geographic characteristics regardless of gender, race, age, and so on? First of all, the results showed that spatial variations in individual accessibility were not directly determined by spatial proximity and opportunity density as suggested by previous accessibility measures. The spatial pattern of individual accessibility was dramatically different from that of urban opportunity density High peaks of accessibility level were found far away from the CBD and regional centers. This finding might be associated with the importance of multi-reference locations and linked travels in shaping accessibility in reality. Furthermore, this study found that spatial patterns of accessibility clearly differ between men and women. These findings suggest that access requires more than proximity, and that the interaction between person-specific space-time constraints and the consequential availability of urban opportunities in space-time renders different accessibility experiences to people even in the same region, which would be one of the key ingredients missing from conventional spatial measures of accessibility.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.8
• /
• pp.71-77
• /
• 2018

In order to estimate behavior of soil mass which is located straight up of reinforced concrete culvert, Ritz method and FEM were applied and arching effects between the soil mass and adjacent soil were considered for the analyses. Analysis results obtained from the Ritz method and finite element method were compared with analytical solution. In the case of estimating nodal forces considered in FEM, caution is needed that shear stress depending on depth from ground surface should be reflected regardless of local coordinate system. Comparing the displacements computed from Ritz method with those of the analytic solution, it is seen that as the power of assumed displacement function increases, differences between the computed displacements and those of analytic solution decreases. It seems that displacements of FEM becomes closer to those of analytical solution as the number of elements are increased. It is seen that stresses computed from the Ritz method don't get closer to those of the analytic solution as the power of assumed displacement function. Stresses from FEM become closer to those of analytic solution as the number of elements are increased. Comparing the analysis results from the Ritz method and FEM with those of analytic solution, it can be seen that FEM is more reliable than Ritz method.

• Progress in Medical Physics
• /
• v.24 no.4
• /
• pp.243-252
• /
• 2013

The aim of this study was to clarify the impacts of acquisition parameters on artifacts in four-dimensional computed tomography (4D CT) images, such as the partial volume effect (PVE), partial projection effect (PPE), and mis-matching of initial motion phases between adjacent beds (MMimph) in cine mode scanning. A thoracic phantom and two cylindrical phantoms (2 cm diameter and heights of 0.5 cm for No.1 and 10 cm for No.2) were scanned using 4D CT. For the thoracic phantom, acquisition was started automatically in the first scan with 5 sec and 8 sec of gantry rotation, thereby allowing a different phase at the initial projection of each bed. In the second scan, the initial projection at each bed was manually synchronized with the inhalation phase to minimize the MMimph. The third scan was intentionally un-synchronized with the inhalation phase. In the cylindrical phantom scan, one bed (2 cm) and three beds (6 cm) were used for 2 and 6 sec motion periods. Measured target volume to true volume ratios (MsTrueV) were computed. The relationships among MMimph, MsTrueV, and velocity were investigated. In the thoracic phantom, shorter gantry rotation provided more precise volume and was highly correlated with velocity when MMimph was minimal. MMimph reduced the correlation. For moving cylinder No. 1, MsTrueV was correlated with velocity, but the larger MMimph for 2 sec of motion removed the correlation. The volume of No. 2 was similar to the static volume due to the small PVE, PPE, and MMimph. Smaller target velocity and faster gantry rotation resulted in a more accurate volume description. The MMimph was the main parameter weakening the correlation between MsTrueV and velocity. Without reducing the MMimph, controlling target velocity and gantry rotation will not guarantee accurate image presentation given current 4D CT technology.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.4
• /
• pp.349-360
• /
• 2008

In this paper, the modeling procedure of random field with an elasto-plastic finite element algorithm and probability of failure on closely-spaced tunnel were investigated. Local average subdivision (LAS) method which can generate discrete random variables fast and accurately as well as change the resolution in certain region was used. And correlated value allocating and weighted average method were suggested to implement geometrical characteristics of tunnel. After the probability of failure on the test problem was thoroughly investigated using random finite element method, the results were compared with the deterministic strength reduction factor method and single random variable method. Of particular importance in this work, is the conclusion that the probability of failure determined by simplified probabilistic analysis, in which spatial variability is ignored by assuming perfect correlation, can be estimated from the safety factor determined by strength reduction factor method. Also, single random variable method can lead to unconservative estimates of the probability of failure.

• Journal of the Korean association of regional geographers
• /
• v.8 no.3
• /
• pp.396-411
• /
• 2002

This paper aims to explore organisational change and learning involving spatial processes and outcomes. In particular, it focuses on the context specific nature of corporate learning and organisational change that can be found in the case of a large Korean firm facing radical economic change. Drawing on the case study of a large Korean firm, the Samsung Electronics Company, three main claims can be followed. First, territorial sources of learning influence the way in which the firm makes use of space/place. Second, corporate learning practices, however, are not based merely on specific localised sources or geographical proximity but on bringing together the local and the global sources by harnessing the properties of relational proximities. It reveals that firms are concerned less on specialising specific local knowledge than promoting organisational knowledge and competences by integrating a variety of knowledge distributed in and out of the boundaries of the firm. Finally, to learn and innovate in a continual basis, firms would attempt to combine codified knowledge with tacit knowledge.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.8 no.4
• /
• pp.307-324
• /
• 2006

Effects of new tunnel construction on an existing tunnel are investigated in this paper. A parametric study was conducted on a number of conditions in terms of relative location of the new tunnel to the existing tunnel using 2D and 3D finite element models. The results indicated that the new tunnel construction imposes most severe effect on the existing tunnel's lining when located below the existing tunnel's springline for cases in which the new tunnel is constructed parallel to the existing tunnel. It is also revealed that the effect to the new tunnel construction is larger when the new tunnel is constructed under the existing tunnel than above for cases in which the new tunnel is crossed with the existing tunnel. Practical implications of the finding are discussed.

• Journal of the Korean Society of Costume
• /
• v.32
• /
• pp.183-200
• /
• 1997

The purpose of this study was to find out the mutual relations of self-efficacy proximity of cosmetic to self and proximity of clothing to self. The researcher used the scale of Sherer Mercadante Maddux Rrentice-Dunn Jacobs and Rogers(1982) for a general and social self-efficacy. The scale of Ryckman Roddins Thorton and Cantrell(1982) for a physical self-efficacy. The researcher corrected and supplemented the tools on the basis of Sontag(1987)'s scale for proximity of clothing to self. The researcher developed proximity of cos-metic to self. The subjects of this study were 172 girl students in the university. The research was analyzed by MANOVA Scheff post hoc test and Cronback a. The Results of this study were as follows: 1. The person who had a higher self-efficacy was higher in the hoy and skin-carve in the sub-causes of proximity of cosmetic to self. There was no difference in social-confidence self-satisfaction and disguise. 2. The person who had a higher self-efficacy was high in the self-expression and the physi-cal satisfaction in the sub-causes of proximity of clothing to self. There was no difference in the joy self-consciousness the consciousness of others and the novelity. 3. The person who had a higher proximity of cosmetic to self was higher in the joy, self-ex-pression and self-consciousness of others and the novelity. There was no difference in the physical satisfaction.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.23 no.6
• /
• pp.1461-1470
• /
• 1998

Bit allocation or quantizer assigning problem is a basic and essential issue in lossy picture coding. It could be represented as minimizing overall distortion with the given constraint that total bits should not exceed allowed bit-budget. Optimal solution can be found by Lagrangian method. However this method needs much computational time and memory. This paper presents an approximation method that uses the activity measure. The comparison between the existing activity measuring techniques are made, and mapping function from activity value to the quantizer is proposed. Under MPEG-1 Intra coding situation, simulations show almost identical results compared to the optimal ones obtained by Lagrangian method with reduced computational time.

• Journal of Korean Society of Transportation
• /
• v.17 no.1
• /
• pp.67-74
• /
• 1999

Where an interchange is located just after a tunnel not only it is impossible to install the traffic signs in tunnel sections but also sufficient sight distance to identify the interchange can't be provided. The objective of this study is to suggest the safety based spacing between tunnel and interchange. For this study accident rate was used as an index representing characteristics for vehicle operation to suggest the appropriate spacing. Traffic volume and the number of accidents on freeway from 1992 to 1997 were analyzed. The relationship between accident rate and spacing represents negative logarithm function such that shorter spacing increases accident rate. An appropriate safety based spacing between tunnel and interchange for four lane freeway with the design speed of 100kph was found as 2.6km.

• Journal of the Korean Society for Railway
• /
• v.20 no.3
• /
• pp.413-422
• /
• 2017

In this study we investigate the importance of the subway station using network centrality measures. For centrality measures, we have used betweenness centrality, closeness centrality, and degree centrality. A new measure called weighted betweenness centrality is proposed, that combines both traditional betweenness centrality and passenger flow between stations. Through correlation analysis and power-law analysis of passenger flow on the Seoul metropolitan subway network, we have shown that weighted betweenness centrality is a meaningful and practical measure. We have also shown that passenger flow between any two stations follows a highly skewed power-law distribution.