• Journal of Power Electronics
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• v.11 no.5
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• pp.662-668
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• 2011

This paper presents an analysis of a 4th order LCLC resonant converter with a capacitive output filter using the state-space approach. The analysis of the converter shows that there are four intervals in a half period. In each interval, the state-space equations are obtained. Due to the soft switching of the converter, an exact equation for the Zero Voltage Switching (ZVS) time and the maximum dead time of the inverter switches are presented. The simulation and experimental results obtained from a 10kv, 370w prototype confirm the validity of the theoretical analysis.

• Coupled systems mechanics
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• v.7 no.3
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• pp.353-371
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• 2018

The Wavenumber or more accurately Wavenumber-FD approach was initially introduced for two-dimensional dynamic analysis of concrete gravity dam-reservoir systems. The technique was formulated in the context of pure finite element programming in frequency domain. Later on, a variation of the method was proposed which was referred to as Wavenumber-TD approach suitable for time domain type of analysis. Recently, it is also shown that Wavenumber-FD approach may be applied for three-dimensional dynamic analysis of concrete arch dam-reservoir systems. In the present study, application of its variation (i.e., Wavenumber-TD approach) is investigated for three-dimensional problems. The method is initially described. Subsequently, the response of idealized Morrow Point arch dam-reservoir system is obtained by this method and its special cases (i.e., two other well-known absorbing conditions) for time harmonic excitation in stream direction. All results for various considered cases are compared against the exact response for models with different values of normalized reservoir length and reservoir base/sidewalls absorptive conditions.

• Bulletin of the Korean Mathematical Society
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• v.44 no.2
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• pp.265-270
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• 2007

The modern approach for wavelets imposes a Bayesian prior model on the wavelet coefficients to capture the sparseness of the wavelet expansion. The idea is to build flexible probability models for the marginal posterior densities of the wavelet coefficients. In this note, we derive exact expressions for a popular model for the marginal posterior density.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.248-251
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• 2003

The ACI 318 stress block parameters have been closely examined for validity of their values in evaluation of flexural strength and deformability. For this the conventional definition of stress block has been used. The comparison of parameter values between ACI stress blocks and the exact approach implies that an alternative idealization other than the rectangular stress block may be required.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6985-6991
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• 2015

Purpose: Various new techniques in thyroid surgery have been developed to improve visualization and reduce risk of complications. New approaches for robotic endoscopic thyroidectomy help to prevent neck scarring and improve surgical ergonomics. The purpose of this study was to compare the efficacy and adventages of an axillo-breast approach (AB group) and an only-axillary approach (OA group) in robotic endoscopic thyroidectomy. Methods: Between November 2008 and July 2014, axillo-breast approach was performed in 128 patients and only-axillary approach was performed in 128 patients for robotic endoscopic thyroidectomy. We compared tumor characteristics, surgical outcomes, and postoperative complications between the two approaches. The homogeneity between two groups of general characteristics was analyzed by independent t-test, fisher's exact test, Chi-square test. Results: There were no differences in terms of tumor characteristics, extent of thyroidectomy, retrieved nodes, and postoperative complications between the two approaches. The patients in OA group can avoid breast scar. Conclusion: Our techniques of AB and OA approaches for robotic endoscopic thyroidectomy are safe, feasible, and cosmetically excellent procedures. Also the OA approach for robotic endoscopic thyroidectomy is an attractive surgical option for patients with thyroid tumor who want an avoid breast scar.

• The Journal of the Korea Contents Association
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• v.17 no.12
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• pp.330-338
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• 2017

The purpose of this study is to examine the effect of blended learning approach on academic achievement and self directed learning skills of nursing undergraduate students. This experimental study is designed for a nonequivalent control group. The number of subjects in this research consists of 145, where 75 of the experimental group participated in blended learning program and 70 of the control group didn't do. The data was analyzed by $x^2$-test, Fisher's exact test, t-test and paired t-test. The effects of blended learning approach on learning outcomes in women's health nursing are as follows : The academic achievement of the experimental group has been more elevated than that of the control group on final examination. The experimental group has made increase in self directed learning skills. The blended learning approach on learning outcomes in nursing major are effective. This study has significant implication in that it identified the availability of the blended learning program and that it would be a useful teaching and learning method to achieve learning outcomes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.3
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• pp.1454-1466
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• 2016

This paper implements an estimated ranking algorithm of closeness centrality measures in large-scale workflow-supported social networks. The traditional ranking algorithms for large-scale networks have suffered from the time complexity problem. The larger the network size is, the bigger dramatically the computation time becomes. To solve the problem on calculating ranks of closeness centrality measures in a large-scale workflow-supported social network, this paper takes an estimation-driven ranking approach, in which the ranking algorithm calculates the estimated closeness centrality measures by applying the approximation method, and then pick out a candidate set of top k actors based on their ranks of the estimated closeness centrality measures. Ultimately, the exact ranking result of the candidate set is obtained by the pure closeness centrality algorithm [1] computing the exact closeness centrality measures. The ranking algorithm of the estimation-driven ranking approach especially developed for workflow-supported social networks is named as RankCCWSSN (Rank Closeness Centrality Workflow-supported Social Network) algorithm. Based upon the algorithm, we conduct the performance evaluations, and compare the outcomes with the results from the pure algorithm. Additionally we extend the algorithm so as to be applied into weighted workflow-supported social networks that are represented by weighted matrices. After all, we confirmed that the time efficiency of the estimation-driven approach with our ranking algorithm is much higher (about 50% improvement) than the traditional approach.

• Steel and Composite Structures
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• v.26 no.4
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• pp.453-461
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• 2018

In this paper, nonlinear vibrations of the unsymmetrical laminated composite beam (LCB) on a nonlinear elastic foundation are studied. The governing equation of the problem is derived by using Galerkin method. Two different end conditions are considered: the simple-simple and the clamped-clamped one. The Hamiltonian Approach (HA) method is adopted and applied for solving of the equation of motion. The advantage of the suggested method is that it does not need any linearization of the problem and the obtained approximate solution has a high accuracy. The method is used for frequency calculation. The frequency of the nonlinear system is compared with the frequency of the linear system. The influence of the parameters of the foundation nonlinearity on the frequency of vibration is considered. The differential equation of vibration is solved also numerically. The analytical and numerical results are compared and is concluded that the difference is negligible. In the paper the new method for error estimation of the analytical solution in comparison to the exact one is developed. The method is based on comparison of the calculation energy and the exact energy of the system. For certain numerical data the accuracy of the approximate frequency of vibration is determined by applying of the suggested method of error estimation. Finally, it has been indicated that the proposed Hamiltonian Approach gives enough accurate result.

• Journal of Communications and Networks
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• v.7 no.4
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• pp.450-461
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• 2005

In this paper, we derive analytical expressions for the exact pairwise error probability (PEP) of a space-time coded system operating over spatially correlated fast (constant over the duration of a symbol) and slow (constant over the length of a code word) fad­ing channels using a moment-generating function-based approach. We discuss two analytical techniques that can be used to evaluate the exact-PEPs (and therefore, approximate the average bit error probability (BEP)) in closed form. These analytical expressions are more realistic than previously published PEP expressions as they fully account for antenna spacing, antenna geometries (uniform linear array, uniform grid array, uniform circular array, etc.) and scattering models (uniform, Gaussian, Laplacian, Von-mises, etc.). Inclusion of spatial information in these expressions provides valuable insights into the physical factors determining the performance of a space-time code. Using these new PEP expressions, we investigate the effect of antenna spacing, antenna geometries and azimuth power distribution parameters (angle of arrival/departure and angular spread) on the performance of a four-state QPSK space-time trellis code proposed by Tarokh et al. for two transmit antennas.

• Steel and Composite Structures
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• v.30 no.1
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• pp.57-67
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• 2019

This paper deals with the static analysis of axially functionally graded rectangular plates. It is assumed that the flexural rigidity of the plate varies exponentially along one of the plate's in-plane dimensions. Both an analytical approach and a numerical method are utilized to solve the problem. The analytical solution is obtained by using the Green's function method. To employ this approach, the adjoint boundary value problem is established. Then, exact solutions for deflection of the plate for different boundary conditions are found. In another way, a finite element formulation for the problem is developed. In order to demonstrate the validity of the Authors' formulation, the results obtained via both mentioned schemes are compared with each other for functionally graded plates and with results of previously published works for homogeneous plates. The effect of plate parameters on the response of the plate is also investigated. To remind the research background, a brief review on the application of Green's function method in plates' analysis and functionally graded plates is also presented.