• Publications of The Korean Astronomical Society
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• v.30 no.3
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• pp.821-832
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• 2015

As a part of the short-period variability survey (SPVS) at Bohyunsan Optical Astronomy Observatory, we obtained time-series BV CCD images in the region of the open cluster NGC 1039 (M34). The observations were performed for 22 nights from July 29, 2008 to September 26, 2010. We also made LOAO observations for 10 days from September 18, 2009 to October 30, 2010 to confirm the small variabilties of ${\delta}$ Scuti-type variable stars. In this paper we presented the observational properties of 28 variable stars found in the region. They are seven ${\delta}$ Scuti-type variable stars, two ${\gamma}$ Doradus-type variable stars, four-teen eclipsing binary stars and five semi-long periodic or slow irregular variables, respectively. Only three variables were listed in the GCVS and the rest are newly discovered ones. We have performed multiple-frequency analysis to determine pulsation frequencies of the ${\delta}$ Scuti-type and ${\gamma}$ Doradus-type variable stars, using the discrete Fourier transform and linear least-square fitting methods. We also have derived the periods and amplitudes of 12 eclipsing binaries from the phase fitting method, and presented the light curves of all variable stars.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.557-560
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• 2010

We have designed a digital variable-focal-length liquid lens by using 4-bit actuators. Each bit actuator consists of 1, 2, 4, and 8 unit actuators, squeezes discrete fluidic volume of $2^4$ different levels into the lens The 4-bit digital actuation mode ($b_4b_3b_2b_1$) affords $2_4$ different lens curvatures and focal lengths. The on/off control of the bit actuators helps in solving the main problem associated with analog liquid lenses, i.e., precise control of the pressure or volume of the fluid for changing the lens curvature and focal length. Experimentally, it has been found that the 4-bit actuators allow 0.074 nl (${\pm}0.02\;nl$) of the given fluid per bit to enter the lens and help in increasing the focal length from 3.63 mm to 38.6 mm in $2^4$ different levels; no high-cost controllers are required for precise control of the pressure or volume in this case. Therefore, the present digital liquid lens is more suitable to integrated optical systems by reducing additional component for pressure and volume control.

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

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.57-65
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• 2009

An efficient and high-fidelity design approach for wing-body shape optimization is presented. Depending on the size of design space and the number of design of variable, aerodynamic shape optimization process is carried out via different optimization strategies at each design stage. In the first stage, global optimization techniques are applied to planform design with a few geometric design variables. In the second stage, local optimization techniques are used for wing surface design with a lot of design variables to maintain a sufficient design space with a high DOF (Degree of Freedom) geometric change. For global optimization, Kriging method in conjunction with Genetic Algorithm (GA) is used. Asearching algorithm of EI (Expected Improvement) points is introduced to enhance the quality of global optimization for the wing-planform design. For local optimization, a discrete adjoint method is adopted. By the successive combination of global and local optimization techniques, drag minimization is performed for a multi-body aircraft configuration while maintaining the baseline lift and the wing weight at the same time. Through the design process, performances of the test models are remarkably improved in comparison with the single stage design approach. The performance of the proposed design framework including wing planform design variables can be efficiently evaluated by the drag decomposition method, which can examine the improvement of various drag components, such as induced drag, wave drag, viscous drag and profile drag.

• Journal of Korea Multimedia Society
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• v.4 no.5
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• pp.423-429
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• 2001

In this paper, we propose the improved method for retrieving images with DC element of DCT that is used in image compression such as JPEG/MPEG. The existing method retrieves images with DC of fixed block size DCT. In this method, the increase in the block size results in faster retrieving speed, but it lessens the accuracy. The decrease in the block size improves the accuracy, however, it degrades the retrieving speed. In order to solve this problem, the proposed method utilizes the variable block size DCT. This method first determines the existence of object regions within each block, and then creates an image region table. Based on this table, it determines the size of each block, following a simple rule; decrease the block size in the object regions, and increase the block size in the background regions. The proposed method using variable block size DCT improves about 15% in terms of the accuracy. Additionally, when there rarely exist images of same pattern, it is able to retrieve faster only by comparing the image region patterns.

• Journal of Korea Multimedia Society
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• v.3 no.4
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• pp.407-415
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• 2000

The ultimate goal of flow control in the semiconductor fabrication process, one of the most equipment-intensive and complex manufacturing process, is to reduce lead time and work in process. In this paper, we propose stand alone layout in the form of job shop using group technology to improve the Productivity and eliminate the inefficiency in FMS (flexible manufacture system). The performance of stand alone layout and in-line layout are analyzed and compared while varying number of device variable chanties. The analysis of in-line layout is obtained by examining its adoption in the memory products of semiconductor factory. The comparison is performed through simulation using ProSys; a window 95 based discrete system simulation software, as a tool for comparing performance of two proposed layouts. The comparison demonstrates that when the number of device variable change is small, in-line layout is more efficient in terms of production Quantity. However, as the number of device variable change is more than 14 times, stand alone layout prevails over in-line layout.

• The Korean Journal of Applied Statistics
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• v.30 no.5
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• pp.615-632
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• 2017

Unlike randomized trial, statistical strategies for inferring the unbiased causal relationship are required in the observational studies. The matching with the propensity score is one of the most popular methods to control the confounders in order to evaluate the effect of the treatment on the outcome variable. Recently, new methods for the causal inference in latent class analysis (LCA) have been proposed to estimate the average causal effect (ACE) of the treatment on the latent discrete variable. They have focused on the application study for the real dataset to estimate the ACE in LCA. In practice, however, the true values of the ACE are not known, and it is difficult to evaluate the performance of the estimated the ACE. In this study, we propose a method to generate a synthetic data using the propensity score in the framework of LCA, where treatment and outcome variables are latent. We then propose a new method for estimating the ACE in LCA and evaluate its performance via simulation studies. Furthermore we present an empirical analysis based on data form the 'National Longitudinal Study of Adolescents Health,' where puberty as a latent treatment and substance use as a latent outcome variable.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.10
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• pp.1887-1894
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• 2016

In the RFID system, the reader transmits a query message to tags in order to identify a unique ID of tags within its detection range. The procedures for arbitrating a collision is essential because the multiple tags can response simultaneously in the same to the query of the Reader. This procedure is known as conflict resolution algorithm and it is a key technology in the RFID system. In this paper, we proposed a variable bits M-ary QT algorithm based on Manchester coding techniques. The proposed algorithm use the location information of the collision bits in the reader and tags. The proposed algorithm can reduce the number of the query-response cycle because it is capable of recognizing discontinuous bits and a variable number of bits. From computer simulation, the proposed method give better performance than the conventional M-ary QT techniques in terms of response, recognition efficiency, communication overhead.

• Archives of Pharmacal Research
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• v.21 no.6
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• pp.634-639
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• 1998

Seven transmembrane segment (7TMS) receptors for chemokines and related molecules have been demonstrated to be essential, in addition to CD4, for HIV and SIV infection. The beta-chemokine receptor CCR5 is the primary, perhaps sole, coreceptor for HIV-1 during the early and chronic phases of infection, and supports infection by most primary HIV-1 and many SIV isolates. Late-stage primary and laboratory-adapted HIV-1, HIV-2, and SIV isolates can use other 7TMS receptors. CXCR4 appears especially important in late-stage HIV infection; several related receptors can also be used. The specificity of SIV viruses is similar. Commonalities among these receptors, combined with analyses of mutated molecules, indicate that discrete, conformationally-depenclent sites on the chemokine receptors determine their association with the third variable and conserved regions of viral envelope glycoproteins. These studies are useful for elucidating the mechanism and molecular determinants of HIV-1 entry, and of inhibitors to that entry.

• Journal of Korean Association for Spatial Structures
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• v.3 no.4 s.10
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• pp.59-67
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• 2003

Genetic algorithm is one of the best ways to solve a discrete variable optimization problem. Genetic algorithm tends to thrive in an environment in which the search space is uneven and has many hills and valleys. In this study, genetic algorithm is used for solving the design problem of gable structure. The design problem of frame structure has some special features(complicate design space, many nonlinear constrants, integer design variables, termination conditions, special information for frame members, etc.), and these features must be considered in the formulation of optimization problem and the application of genetic algorithm. So, 'FRAME operator', a new genetic operator for solving the frame optimization problem effectively, is developed and applied to the design problem of gable structure. This example shows that the new opreator has the possibility to be an effective frame design operator and genetic algorithm is suitable for the frame optimization problem.