• Honam Mathematical Journal
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• v.45 no.2
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• pp.300-315
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• 2023

In this article, we deal with the biharmonicity of a vector field X viewed as a map from a pseudo-Riemannian manifold (M, g) into its tangent bundle TM endowed with the Sasaki metric g_S. Precisely, we characterize those vector fields which are biharmonic maps, and find the relationship between them and biharmonic vector fields. Afterwards, we study the biharmonicity of left-invariant vector fields on the three dimensional Heisenberg group endowed with a left-invariant Lorentzian metric. Finally, we give examples of vector fields which are proper biharmonic maps on the Gödel universe.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2008.10a
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• pp.279-285
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• 2008

• Journal of the Korean Mathematical Society
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• v.23 no.2
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• pp.135-140
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• 1986

• Electrical & Electronic Materials
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• v.13 no.9
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• pp.13-17
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• 2000

• 한국도로학회:학술대회논문집
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• 2008.10a
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• pp.513-517
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• 2008

• Journal of Korean Society of Steel Construction
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• v.26 no.3
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• pp.143-154
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• 2014

An improved method for evaluating effective buckling length of semi-rigid frame with inelastic behavior is newly proposed. Also, generalized exact tangential stiffness matrix with rotationally semi-rigid connections is adopted in previous studies. Therefore, the system buckling load of structure with inelastic behaviors can be exactly obtained by only one element per one straight member for inelastic problems. And the linearized elastic stiffness matrix and the geometric stiffness matrix of semi-rigid frame are utilized by taking into account 4th terms of taylor series from the exact tangent stiffness matrix. On the other hands, two inelastic analysis programs(M1, M2) are newly formulated. Where, M1 based on exact tangent stiffness matrix is programmed by iterative determinant search method and M2 is using linear algorithm with elastic and geometric matrices. Finally, in order to verify this present theory, various numerical examples are introduced and the effective buckling length of semi-rigid frames with inelastic materials are investigated.

• International Journal of Highway Engineering
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• v.14 no.4
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• pp.149-162
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• 2012

PURPOSES : The causes of traffic accidents can be classified into the factors of highway users, vehicles, and driving environments. Traffic accidents result from the deficiency in single or combination of these three factors. The objective of this study is to define the "potentially hazardous sections of highway" in terms of traffic safety considering these three factors. METHODS : The test drivers performed repeated driving on these highway sections. The drivers and passengers recorded the sections on which the driving was uncomfortable, and the speeds on the sections excluding the uncomfortable sections were used for the development of the model. RESULTS : The model is composed of three sub-models for each of the horizontal curve, tangent, and the section where the curve starts/ends. The safe driving behavior coefficients by the horizontal curvature were derived by comparing the maximum operating speeds at which the vehicle may slide or deviate and the speeds at which the drivers feel comfort. The safety speeds on tangent were derived by the length of tangent section considering the driver's desired speeds under the traffic condition on which the drivers hardly influenced by the other vehicles. For the sections where the curve starts/ends, the driving behaviors were classified by the distances between the curves, and the safe acceleration/deceleration speeds were derived on which the drivers enter/exit the curve sections safely. CONCLUSIONS : Safety speed could then be regarded that the model suggested in this study may be useful to define the potentially hazardous highway section and contribute the improvement of highway safety.

• Progress in Superconductivity
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• v.4 no.2
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• pp.137-143
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• 2003

In measuring the microwave surface resistance of high-Tc superconductor (HTS) films using the dielectric-loaded cavity resonator method, one of the most important factors that limit the measurement sensitivity is the measurement error in the loss tangent ($tan\delta$) of the dielectric rod placed inside the cavity. We have measured the effective surface resistance ( $R_{S}$ $^{eff}$) of$ YBa_2$$_Cu3$$_{7-{\delta}}$ (YBCO) films and the $tan\delta$ of rutile ($TiO_2$) using the 'two-tone'method suggested by Kobayashi et at. [IEEE, MTT-S Digest, 495, (2001)], which enables simultaneous measurements of both the $R_{S}$ $^{eff}$ fof HTS films and the $tan\delta$ of the rutile with high sensitivity. A rutile-loaded cavity resonator with the $TE_{012}$ and $TE_{021}$ resonant frequencies at 13.67 - 14.01 GHz is used for this purpose. At temperatures where the two modes do not couple with other modes, the $R_{S}$ $^{eff}$ of YBCO films and $tan\delta$ of rutile measured by the two-tone method appear to match well with the corresponding values measured using the reported $tan\delta$ values of sapphire within 10 %. Usefulness of the 'two-tone' method for microwave characterization of HTS films and dielectrics is discussed.d.ielectrics is discussed.ussed.

• The Journal of the Korea Contents Association
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• v.9 no.2
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• pp.97-105
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• 2009

This paper presents a combination of the generalized Cascade Correlation and generalized Recurrent Cascade Correlation learning algorithms. The new network will be able to grow with vertical or horizontal direction and with recurrent or without recurrent units for the quick solution of the pattern classification problem. The proposed algorithm was tested learning capability with the sigmoidal activation function and hyperbolic tangent activation function on the contact lens and balance scale standard benchmark problems. And results are compared with those obtained with Cascade Correlation and Recurrent Cascade Correlation algorithms. By the learning the new network was composed with the minimal number of the created hidden units and shows quick learning speed. Consequently it will be able to improve a learning capability.

• Journal of Advanced Navigation Technology
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• v.13 no.1
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• pp.41-47
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• 2009

In this paper, a band pass filter with a rejection band is proposed for UWB(Ultra Wide Band) communication system. First, low pass filter accessed cut off frequency of 10.2 GHz was designed using structure stepped impedance. And high pass filter accessed cut of frequency of 3.2 GHz was designed using parallel short-stub. There was implemented composite connection of designed low pass filter and high pass filter. The relative dielectric constant, the height, the loss tangent of the PCB substrate were ${\varepsilon}_r$=2.2, h=0.508 mm and loss tangent = 0.0009 respectively. The fabricated band pass filter shows a compact size of 3 cm. The fabricated band pass filter was characterized using 37169A VNA(Vector Network Analyzer). And measured result were obtained 7.5 GHz of bandwidth and -10 dB of return loss and -3 dB of insertion loss from pass band. The result of the research can be used for the UWB communications and MIC/MMIC, RFIC system.