• Journal of the Korean Geographical Society
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• v.45 no.3
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• pp.319-341
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• 2010

The purposes of this study are to classify heavy snowfall types in the Republic of Korea based on fresh snowfall data and atmospheric circulation data during the last 36(1973/74-2008/09) snow seasons and to identify typical surface synoptic climate patterns that characterize each heavy snowfall type. Four synoptic climate categories and seventeen regional heavy snowfall types are classified based on sea level pressure/surface wind vector patterns in East Asia and frequent spatial clustering patterns of heavy snowfall in the Republic of Korea, respectively. Composite analyses of multiple surface synoptic weather charts demonstrate that the locations and intensity of pressure/wind vector mean and anomaly cores in East Asia differentiate each regional heavy snowfall type in Korea. These differences in synoptic climatic fields are primarily associated with the surge of the Siberian high pressure system and the appearance of low pressure systems over the Korean Peninsula. In terms of hemispheric atmospheric circulation, synoptic climatic patterns in the negative mode of winter Arctic Oscillation (AO) are also associated with frequent heavy snowfall in the Republic of Korea at seasonal scales. These results from long-term synoptic climatic data could contribute to improvement of short-range or seasonal prediction of regional heavy snowfall.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.6
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• pp.87-95
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• 1999

We propose a simulation model of 3-dimensional MPEG data over Asynchronous transfer Mode(ATM) networks. The model is based on a slice level and is named to Projected Vector Autoregressive(PVAR) model. The PVAR model is modeled using the Autoregressive(AR) model in order to meet the autocorrelation condition and fit the histogram, and maps real data by a projection function. For the projection function, we use the Cumulative Distribution Probability Function (CDPF), and the procedure is performed at each slice level. Our proposed model shows good performance in meeting the autocorrelation condition and fitting the histogram, and is found important in analyzing the performance of networks. In addiotion, we apply a smoothing method by which a periodic mean value. In general. the Quality of Service(QoS) depends on the Cell Loss Rate(CLR), which is related to the cell loss and a maximum delay in a buffer. Hence the proposed smoothing method can be used to improve the QoS.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.1
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• pp.44-54
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• 2001

In this paper, a novel test method is proposed to detect the hard and soft fault in analog circuits. The proposed test method makes use of the offset voltage, which is one of the op-amps characteristics. During the test mode, CUT is modified to unit gain op-amps with feedback loop. When the input of the op-amp is grounded, a good circuit has a small offset voltage, but a faulty circuit has a large offset voltage. Faults in the op-amp which cause the offset voltage exceeding predefined range of tolerance can be detected. In the proposed method, no test vector is required to be applied. Therefore the test vector generation problem is eliminated and the test time and cost is reduced. In this note, the validity of the proposed test method has been verified through the example of the dual slope A/D converter. The HSPICE simulations results affirm that the presented method assures a high fault coverage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.408-422
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• 2000

In this paper, we propose a generalized vector channel model for wireless communication systems using antenna arrays. The proposed channel model reflects path loss. spatial-temporal variation of shadowing, multipath fading , Doppler effect, spatial distribution of local scatterers and delay spread due to remote dominant scatterers. In addition, we use a discrete ray model in which respective ray signal experiences independent shadowing, fading and Doppler shift, and impinges on antenna arrays at a distinct angle. Based on the proposed mode. we derive the relations on the spatial and temporal correlations of the received signals and implement a spatial channel simulator. By comparing the theoretical values with the simulated ones, we verify the effectiveness of the implemented simulator. The simulator is then used to generate an arbitrary channel impulse response and to analyze the channel characteristics under various environments.

• Smart Structures and Systems
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• v.14 no.2
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• pp.145-158
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• 2014

The objective of this study is to improve the survivability and reliability of the FBG sensor network in the structural health monitoring (SHM) system. Therefore, a model reconstruction soft computing recognition algorithm based on support vector regression (SVR) is proposed to achieve the high reliability of the FBG sensor network, and the grid search algorithm is used to optimize the parameters of SVR model. Furthermore, in order to demonstrate the effectiveness of the proposed model reconstruction algorithm, a SHM system based on an eight-point fiber Bragg grating (FBG) sensor network is designed to monitor the foreign-object low velocity impact of a CFRP composite plate. Simultaneously, some sensors data are neglected to simulate different kinds of FBG sensor network failure modes, the predicting results are compared with non-reconstruction for the same failure mode. The comparative results indicate that the performance of the model reconstruction recognition algorithm based on SVR has more excellence than that of non-reconstruction, and the model reconstruction algorithm almost keeps the consistent predicting accuracy when no sensor, one sensor and two sensors are invalid in the FBG sensor network, thus the reliability is improved when there are FBG sensors are invalid in the structural health monitoring system.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.2
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• pp.83-92
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• 2007

In connectionless packet network, if a sender encrypts packets by block chaining mode and send it to receiver, the receiver should decrypt packets in encrypted order that is not received order. Therefore, the performance and efficiency are lowered for crypto communication system. To solve this problem, we propose packet encryption scheme for connectionless packet network that can decrypt the packets independently, even if the received order of packets are changed or packets are missed. The scheme makes new IV(Initial Vector) using IV that created by key exchange process and salt that made by random number. We propose extended Cryptoki API that added packet encryption/decryption functions and mechanism for improving convenience and performance. We implement the scheme and get result that the performance increased about $1.5{\sim}l5.6$ times compare with in case of implementing using Cryptoki API in the test environment.

• Journal of Korean Society of Transportation
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• v.23 no.1
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• pp.103-114
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• 2005

The transit fare resulted from the renovation of public transit system in Seoul is basically determined based on the distance-based fare policy (DFP). In DFP, the total fare a passenger has to pay for is calculated by the basic-transfer-premium fare decision rule. The fixed amount of the basic fare is first imposed when a passenger get on a mode and it lasts within the basic travel distance. The transfer fare is additionally imposed when a passenger switches from one mode to another and the fare of the latter mode is higher than the former. The premium fare is also another and the fare of the latter begins to exceed the basic travel distance and increases at the proportion of the premium fare distance. The purpose of this study is to propose an algorithm for finding K number of paths, paths that are sequentially sorted based on total amount of transit fare, under DFP of the idstance-based fare policy. For this purpose, the link mode expansion technique is proposed in order to save notations associated with the travel modes. Thus the existing K shortest path algorithms adaptable for uni-modal network analysis are applicable to the analysis for inter-modal transportation networks. An optimality condition for finding the K shortest fare routes is derived and a corresponding algorithms is developed. The case studies demonstrate that the proposed algorithm may play an important role to provide diverse public transit information considering fare, travel distance, travel time, and number of transfer.

• Korean Journal of Remote Sensing
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• v.21 no.2
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• pp.121-133
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• 2005

Texture imaging, which means texture image creation by co-occurrence relation, has been known as one of the useful image analysis methodologies. For this purpose, most commercial remote sensing software provides texture analysis function named GLCM (Grey Level Co-occurrence Matrix). In this study, texture-imaging program based on GLCM algorithm is newly implemented. As well, texture imaging modules for GLDV (Grey Level Difference Vector) are contained in this program. As for GLCM/GLDV Texture imaging parameters, it composed of six types of second order texture functions such as Homogeneity, Dissimilarity, Energy, Entropy, Angular Second Moment, and Contrast. As for co-occurrence directionality in GLCM/GLDV, two direction modes such as Omni-mode and Circular mode newly implemented in this program are provided with basic eight-direction mode. Omni-mode is to compute all direction to avoid directionality complexity in the practical level, and circular direction is to compute texture parameters by circular direction surrounding a target pixel in a kernel. At the second phase of this study, some case studies with artificial image and actual satellite imagery are carried out to analyze texture images in different parameters and modes by correlation matrix analysis. It is concluded that selection of texture parameters and modes is the critical issues in an application based on texture image fusion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Journal of Korean Association for Spatial Structures
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• v.11 no.2
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• pp.81-88
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• 2011

The studies of seismic response control are mainly conducted on rahmen structure until now. Spatial structures have the different dynamic characteristics from general rahmen structures. So, the results of these studies are very limited for vibration control and seismic design of spatial structures. TMD(Tuned Mass Damper) is one of the vibration control device that is mainly used to reduce the vibration level of high-rised building, bridge or stadium structure. In this study, an arch structure was used as an example structure because it has primary characteristics of spatial structures and the seismic behaviour of spatial structures may fundamentally differ from the conventional building structures. So, the vibration control performance is evaluated according to the change of TMD mass and TMD location. It is reasonable to install TMD at the quarter point that is dominant mode vector of 1st mode, And it is appropriate that TMD mass ratio is 2% in the seismic response control of arch structure.