• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1C
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• pp.67-77
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• 2007

Virus throttling technique, one of many early worm detection techniques, detects Internet worm propagation by limiting connect requests within a certain ratio. The typical virus throttling controls the period of rate limiter autonomically by utilizing weighted average delay queue length to reduce connection delay time without hanving a large effect on worm detection time. In the existing virus throttling research, a minimum period of variable rate limiter is fired and a turning point which is a point that the period of rate limiter has been being decreased and starts to be increased is also fixed. However, these two performance factors have different effects on worm detection time and connection delay. In this paper, we analyze the effect of minimum period and turning point of variable rate limiter, and then propose an algorithm which determines values of performance factors by referencing current traffic pattern. Through deep experiments, it is verified that the proposed technique is more efficient in respect of reducing worm detection time and connection delay than the existing virus throttling which fixed the performance factors.

• Journal of Power Electronics
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• v.13 no.6
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• pp.1016-1023
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• 2013

Predictive current control offers the potential for achieving more precise current control with a minimum of distortion and harmonic noise. However, the predictive method is difficult to implement and has a greater computational burden. This paper introduces a theoretical analysis and experimental verification for an improved predictive current control technique applied to single phase grid connected voltage source inverters (VSI). The proposed technique has simple calculations. An ATmega1280 microcontroller board is used to implement the proposed technique for a simpler and cheaper control system. To enhance the current performance and to obtain a minimum of current THD, an improved tri-level PWM switching strategy is proposed. The proposed switching strategy uses six operation modes instead of four as in the traditional strategy. Simulation results are presented to demonstrate the system performance with the improved switching strategy and its effect on current performance. The presented experimental results verify that the proposed technique can be implemented using fixed point 8-bit microcontroller to obtain excellent results.

• The Journal of Advanced Prosthodontics
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• v.12 no.3
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• pp.173-180
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• 2020

PURPOSE. This study compared digital (reference point matching) and replica methods for measuring marginal and internal fit of full coverage restorations. MATERIALS AND METHODS. A maxillary left first molar typodent was fixed on to an aluminum base and prepared to receive all-ceramic full coverage restoration. The model was scanned with an intraoral scanner (CEREC Omnicam, Sirona, York, PA, USA). Twelve crowns were fabricated from lithium disilicate blocks (IPS emax CAD, Ivoclar Vivadent) and then crystalized. Marginal and internal fit of each restoration was measured by two examiners using replica and a new digital three-dimensional technique. Reliability between the two methods and two examiners was assessed by correlation and Cronbach's Alpha coefficient (P<.05). A Bland-Altman assessment for agreement was used to compare the two methods. RESULTS. Bland-Altman assessment showed that the mean of difference for marginal, absolute marginal, and axial gap was respectively -1.04 ㎛, -41.9 ㎛, and -29.53 ㎛ with limit of agreement (LOA) between -37.26 to 35.18 ㎛ for marginal, -105.85 to 22.05 ㎛ for absolute marginal and -80.52 to 22.02 ㎛ for axial gap. Positive correlation for repeatability (P<.05) in determining marginal and internal gaps by the two examiners in both techniques was revealed. Reliability of both techniques in all sites of measurements was at least good (0.8 ≤ α < 0.9). CONCLUSION. Both measuring techniques appeared highly reliable for evaluating fit of fixed dental restorations, while reference point matching provided higher values in axial and absolute marginal gap assessment.

• Geomechanics and Engineering
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• v.18 no.3
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• pp.235-245
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• 2019

This paper presents a novel methodology for face stability assessment of rock tunnels under water table by combining the kinematical approach of limit analysis and numerical simulation. The tunnels considered in this paper are excavated in fractured rock masses characterized by the Hoek-Brown failure criterion. In terms of natural rock deposition, a more convincing case of depth-dependent mi, GSI, D and ${\sigma}_c$ is taken into account by proposing the horizontally layered discretization technique, which enables us to generate the failure surface of tunnel face point by point. The vertical distance between any two adjacent points is fixed, which is beneficial to deal with stability problems involving depth-dependent rock parameters. The pore water pressure is numerically computed by means of 3D steady-state flow analyses. Accordingly, the pore water pressure for each discretized point on the failure surface is obtained by interpolation. The parametric analysis is performed to show the influence of depth-dependent parameters of $m_i$, GSI, D, ${\sigma}_c$ and the variation of water table elevation on tunnel face stability. Finally, several design charts for an undisturbed tunnel are presented for quick calculations of critical support pressures against face failure.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.4
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• pp.309-324
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• 1987

In recent years has been an increasing interest with respect to using the discrete cosine transform(DCT) of which performance is found close to that of the Karhumen-Loeve transform, known to be optimal in the area of digital image processing for tha purpose of the image data compression. Among most of reported algorithms aimed at lowering the coputation complexity. Chen's algorithm is is found to be most popular, Recently, Lee proposed a now algorithm of which the computational complexity is lower than that of Chen's. but its performance is significantly degraded by FWL(Finite-Word-Lenght) effects as a result of employinga a fixed-poing arithmetic. In this paper performance evaluation of these two algorithms and error analysis of FWL effect are described. Also a scaling technique which we call Up & Down-scaling is proposed to allevaiate a performance degradation due to fixed-point arithmetic. When the 16x16point 2DCT is applied on image data and a 16-bit fixed-point arithmetic is employed, both the analysis and simulation show that is colse to that of Chen's.

• Journal of Power Electronics
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• v.14 no.1
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• pp.156-164
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• 2014

The power-voltage (P-V) characteristic of a photovoltaic (PV) array is nonlinear and time varying with the change in atmospheric conditions. As a result, the maximum power point tracking (MPPT) technique must be applied in PV systems to maximize the generated energy. The incremental conductance (INC) algorithm, one of the MPPT strategies, is widely used for its high tracking accuracy, good adaptability to rapidly changing atmospheric conditions, and easy implementation. This paper presents a modified asymmetrical variable step size INC MPPT method that is based on the asymmetrical feature of the P-V curve. Compared with conventional fixed or variable step size method, the proposed method can effectively improve tracking accuracy and speed. The theoretical foundation and design principle of the proposed approach are validated by the simulation and experimental results.

• Journal of Power Electronics
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• v.16 no.1
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• pp.277-286
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• 2016

This paper offers two Maximum Power Point Tracking (MPPT) systems for Photovoltaic (PV) applications. The first MPPT method is based on a fixed frequency Model Predictive Control (MPC). The second MPPT technique is based on the Predictive Hysteresis Control (PHC). An experimental demonstration shows that the proposed techniques are fast, accurate and robust in tracking the maximum power under different environmental conditions. A DC/DC converter with a high voltage gain is obligatory to track PV applications at the maximum power and to boost a low voltage to a higher voltage level. For this purpose, a high gain Switched Inductor Quadratic Boost Converter (SIQBC) for PV applications is presented in this paper. The proposed converter has a higher gain than the other transformerless topologies in the literature. It is shown that at a high gain the proposed SIQBC has moderate efficiency.

• Proceedings of the IEEK Conference
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• 2000.11d
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• pp.81-84
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• 2000

Cellular automata are discrete dynamical systems whose behaviour is completely specified in terms of a local relation. If cellular automata convergence to fixed points, then it can be used to image processing. From the generalized Potts automata point of view, we propose in this paper a cellular automata technique for reducing image noise. To minimize blurring effect, an algorithm based on neighborhood median computation is Preferred. Experimental results are reported.

• East Asian mathematical journal
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• v.28 no.5
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• pp.561-567
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• 2012

The approximate solvability of a generalized system for relaxed cocoercive extended general variational inequalities is studied by using the project operator technique. The results presented in this paper are more general and include many previously known results as special cases.

• Journal of the Korean Mathematical Society
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• v.43 no.2
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• pp.445-459
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• 2006

In this paper cellular neural networks with continuously distributed delays are considered. Sufficient conditions for the existence and exponential stability of the almost periodic solutions are established by using fixed point theorem, Lyapunov functional method and differential inequality technique. The results of this paper are new and they complement previously known results.