• Journal of Electrical Engineering and Technology
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• v.8 no.2
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• pp.197-205
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• 2013

Real time transient stability assessment mainly depends on real-time prediction. Unfortunately, conventional techniques based on offline analysis are too slow and unreliable in complex power systems. Hence, fast and reliable stability prediction methods and simple stability criterions must be developed for real time purposes. In this paper, two new methods for real time determining critical clearing time based on clustering identification are proposed. This article is covering three main sections: (i) clustering generators and recognizing critical group; (ii) replacing the multi-machine system by a two-machine dynamic equivalent and eventually, to a one-machine-infinite-bus system; (iii) presenting a new method to predict post-fault trajectory and two simple algorithms for calculating critical clearing time, respectively established upon two different transient stability criterions. The performance is expected to figure out critical clearing time within 100ms-150ms and with an acceptable accuracy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.327-333
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• 1998

The influence of slow cooling and annealing time in $O_2$in MPEG process on $J_c$ was investigated. From the measurement of $J_c$,SEM and XRD, it was observed that the critical current density was related with the slow cooling time and annealing time in $O_2$. The value of $J_c$ was the highest at slow cooling time of 40 hour. And also, the value of $J_c$ along the annealing time in $O_2$in the case of the slow cooling time of 40 hours was inclined to increase with annealing time. Consequently, it can be suggested that proper slow cooling time and annealing time after slow cooling in MPMG process be important to improve the critical characteristics.

• Quality Improvement in Health Care
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• v.9 no.1
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• pp.66-73
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• 2002

The current health care system demands provisions for patient care in perspectives of a cost-effectiveness and patient satisfaction. Critical pathway implementation facilitates optimal sequencing and intervention timing of patient care, and makes medical team and patients participate in a treatment actively. In this study, a critical pathway was developed and implemented to patients with osmidrosis who undertake operation. Sixty patients were included in the study. The critical pathway was implemented for care of 26 patients while the traditional care was implemented for 34 patients. In the critical pathway implemented group, time needed for charting and unessential working was reduced. Mean time amount of time for patient nursing was increased. The critical pathway implementation is an effective method to utilize time of medical team. Also it increases the satisfaction index of patients and medical team simultaneously.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.2
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• pp.246-255
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• 1998

This paper presents a novel method for real-time malfunction detection of plasma etching process using EPD signal traces. First, many reference EPD signal traces are collected using monochromator and data acquisition system in normal etching processes. Critical points are defined by applying differentiation and zero-crossing method to the collected reference signal traces. Critical parameters such as intensity, slope, time, peak, overshoot, etc., determined by critical points, and frame attributes transformed signal-to symbol of reference signal traces are saved. Also, UCL(Upper Control Limit) and LCL(Lower Control Limit) are obtained by mean and standard deviation of critical parameters. Then, test EPD signal traces are collected in the actual processes, and frame attributes and critical parameters are obtained using the above mentioned method. Process malfunctions are detected in real-time by applying SPC(Statistical Process Control) method to critical parameters. the Real-time malfunction detection method presented in this paper was applied to actual processes and the results indicated that it was proved to be able to supplement disadvantages of existing quality control check inspecting or testing random-selected devices and detect process malfunctions correctly in real-time.

• Structural Engineering and Mechanics
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• v.14 no.6
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• pp.661-677
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• 2002

The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

• Journal of Korean Society of Transportation
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• v.19 no.6
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• pp.195-205
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• 2001

The objective of the paper is to analyze the traffic characteristics for freeway merging area. Freeway merging area is different from basic section due to ramp vehicles. Therefore, to understand the traffic characteristics of (leeway merging area, this study focused on two factors including critical time headway required in merging maneuver and maximum possible merging volume. In this paper, new model that adopts critical time headway instead of critical time gap in calculating the maximum possible merging volume based on probability function was developed In previous studies, for calculating the maximum possible merging volume, it was considered that merging vehicles could merge freely if a given time gap was greater than the critical time gap. Also, the critical time gap was used as the same value in all traffic flow conditions. But, a time gap required in merging maneuver could be changed, even to the same driver, because difference of relative speed varies in different traffic flow conditions. So, in some cases, the critical time gap could be insufficient value in merging maneuver. Therefore, in this study. a calculating procedure for critical time headway in all traffic flow conditions was presented. Also, the maximum possible merging volume and capacity for freeway merging area were calculated by using the previously found critical time headway.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.185-188
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• 1997

The influence of slow cooling and annealing time in $O_2$ during melting and growth step in MPMG process on J$_{c}$ was investigated. Through the measurement of J$_{c}$ SEM and XRD, it can be observed that the critical characteristics were related with the slow cooling time and annealing time in 02 for melting and growth step of MPMG process. The distribution of critical current density with slow cooling time was the porabolic form and the value of J. was the highest at the 40 hour slow cooling time. And also, the value of J$_{c}$, along the annealing time in $O_2$ in the case of the slow cooling time 40 hour was inclined to increase with annealing time. Consequently, it can be suggested that proper slow cooling titre and annealing time along slow cooling in MPMG process be important to improve the critical characteristics.stics.

• Structural Engineering and Mechanics
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• v.13 no.3
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• pp.329-343
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• 2002

In this research, the dynamic stability of an orthotropic elastic conical shell, with elasticity moduli and density varying in the thickness direction, subject to a uniform external pressure which is a power function of time, has been studied. After giving the fundamental relations, the dynamic stability and compatibility equations of a nonhomogeneous elastic orthotropic conical shell, subject to a uniform external pressure, have been derived. Applying Galerkin's method, these equations have been transformed to a pair of time dependent differential equations with variable coefficients. These differential equations are solved using the method given by Sachenkov and Baktieva (1978). Thus, general formulas have been obtained for the dynamic and static critical external pressures and the pertinent wave numbers, critical time, critical pressure impulse and dynamic factor. Finally, carrying out some computations, the effects of the nonhomogeneity, the loading speed, the variation of the semi-vertex angle and the power of time in the external pressure expression on the critical parameters have been studied.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2007.11a
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• pp.68-74
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• 2007

Critical Chain Project Management(CCPM) is a new project management system paradigm which maintains the advantages of PERT/CPM and improves the shortcomings of it. In CCPM the task durations are determined as 50% time estimates, ie average time discarding the their contingency. CCPM determines the critical chain the constraint of a projects considering the logical precedence relationship and resource conflict resolution. Project buffer is located at the end of critical chain to absorb the variations of critical chain. The size of project buffer is usually calculated as the half of the sum of critical chain length. Also feeding buffer is inserted after each non-critical chain which feeding into the critical chain to prevent the time delay of critical chain from uncertainties of non-critical chains. Resource buffer can be utilized to improve the availability of resources of critical chain. Buffer management is a project execution and control mechanism. Buffers are classified into 3 zones. They are OK zone, Watch and Plan zone and Expediting zone. If the project status is within Watch and Plan zone, contingency plan is established. And if it changes into Expediting zone, the preplanned contingency plan are executed to recover the time delay. In CCPM the workers are asked to work with relay runner work mechanism that they work fast if possible and report their completion to project manager for the succeeding task to start as soon as possible. The task durations are not considered as the promised time schedule. The multi-tasking is prohibited.

• Structural Engineering and Mechanics
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• v.26 no.6
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• pp.687-707
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• 2007

High-tech facilities engaged in the production of semiconductors and optical microscopes are extremely expensive, which may require time-domain analysis for seismic resistant design in consideration of the most critical directions of seismic ground motions. This paper presents a framework for generating three-dimensional critical seismic ground acceleration time histories compatible with the response spectra specified in seismic design codes. The most critical directions of seismic ground motions associated with the maximum response of a high-tech facility are first identified. A new numerical method is then proposed to derive the power spectrum density functions of ground accelerations which are compatible with the response spectra specified in seismic design codes in critical directions. The ground acceleration time histories for the high-tech facility along the structural axes are generated by applying the spectral representation method to the power spectrum density function matrix and then multiplied by envelope functions to consider nonstationarity of ground motions. The proposed framework is finally applied to a typical three-story high-tech facility, and the numerical results demonstrate the feasibility of the proposed approach.