• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.615-622
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• 2017

A normal shock wave is initially formed in the shock tube that migrates towards the closed end of the tube, which, in turn, leads to the reflection of shock. Due to the interaction of the reflected shock with the boundary layer, bifurcation of the shock wave takes place. A shock train will be generated after the bifurcated shock wave approaches the contact surface. Until now, only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study, a CFD analysis has been performed on a two dimensional axisymmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of the shock train phenomenon, quantitative studies have been performed by varying shock tube length, diameter under fixed diaphragm, and pressure ratio inside a shock tube.

• The Korean Journal of Applied Statistics
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• v.29 no.1
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• pp.181-192
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• 2016

We consider several methods to approximate option prices with correction terms to the Black-Scholes option price. These methods are able to compute option prices from various risk-neutral distributions using relatively small data and simple computation. In this paper, we compare the performance of Edgeworth expansion, A-type and C-type Gram-Charlier expansions, a method of using Normal inverse gaussian distribution, and an asymptotic method of using nonlinear regression through simulation experiments and real KOSPI200 option data. We assume the variance gamma model in the simulation experiment, which has a closed-form solution for the option price among the pure jump $L{\acute{e}}vy$ processes. As a result, we found that methods to approximate an option price directly from the approximate price formula are better than methods to approximate option prices through the approximate risk-neutral density function. The method to approximate option prices by nonlinear regression showed relatively better performance among those compared.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5301-5323
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• 2017

Small cell deployment offers a low-cost solution for the boosted traffic demand in heterogeneous cellular networks (HCNs). Besides improved spatial spectrum efficiency and energy efficiency, future HCNs are also featured with the trend of network architecture convergence and feasibility for flexible mobile applications. To achieve these goals, dual connectivity (DC) is playing a more and more important role to support control/user-plane splitting, which enables maintaining fixed control channel connections for reliability. In this paper, we develop a tractable framework for the downlink SINR analysis of DC assisted HCN. Based on stochastic geometry model, the data-control joint coverage probabilities under multi-frequency and single-frequency tiering are derived, which involve quick integrals and admit simple closed-forms in special cases. Monte Carlo simulations confirm the accuracy of the expressions. It is observed that the increase in mobility robustness of DC is at the price of control channel SINR degradation. This degradation severely worsens the joint coverage performance under single-frequency tiering, proving multi-frequency tiering a more feasible networking scheme to utilize the advantage of DC effectively. Moreover, the joint coverage probability can be maximized by adjusting the density ratio of small cell and macro cell eNBs under multi-frequency tiering, though changing cell association bias has little impact on the level of the maximal coverage performance.

• Physical Therapy Korea
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• v.5 no.3
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• pp.34-41
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• 1998

Noninvasive low intensity ultrasound has been shown to be an effective means of accelerating bone fracture repair in both animal and clinical studies. The effects of ultrasound stimulation on bone repair after fibular osteotomy were assessed in a rabbit fibular fracture model. Bilateral closed fibular fractures were made in skeletally mature male White Japanese rabbits. In this study, 24 subjects were randomly divided into 2 groups: experimental group 1 (n=12), and experimental group 2 (n=12). Experimental group 1 received 0.875 MHz continuous ultrasound and Experimental group 2 was treated with 3 MHz continuous u1trasound. The ultrasound intensity was 50 $mW/cm^2$ and treatment time was 10 minutes for every session in both groups. In each rabbit, one fibula served as a control and the other was subjected to ultrasound treatment 5 times per week for 3 weeks. After 3 weeks, rabbits were sacrificed and the ratios of the area between the trabeculae and bone marrow of the fibulae were calculated. At the end of the experimental period, 14 of the 24 rabbits were excluded due to complications from surgery or inadequate fracture status for this study. There was no statistically significant difference in the trabeculae area between experimental leg and control leg in experimental group 1 and experimental group 2 (p>0.05). And there was also no statistic-statistically significant difference between experimental group 1 and experimental group 2 according to ultrasound treatment frequencies, 0.875 MHz and 3 MHz (p>0.05). These data suggest that in Japanese white rabbits, low intensity ultrasound stimulation does not facilitate fracture repair nor is there any difference in fracture repair results between ultrasound frequencies, 0.875 MHz and 3 MHz.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.2
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• pp.105-110
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• 1990

In this paper, a compliance robot control algorithm using a PID adaptive controller is proposed. The compliance robot is suitable for the tasks in contact with environment, such as assembly operation or surface processing. A hybrid robot control method can control force and position simultaneously and two independant feedback closed loops are formed in this method. Because the compliance robot is operated in contact with environment, it is very difficult to obtain linear model of dynamics for this robot. In order to overcome this difficulty, a PID adaptive controller independant of robot dynamics is applied to the compliance robot. The proposed control algorithm for the compliance robot was analyzed and conformed by simulating the surface processing task by a two-joint robot.

• Safety and Health at Work
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• v.11 no.1
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• pp.50-60
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• 2020

Background: The relationship between risk factors and likelihood of occupational injury has been studied. However, what has been published has only provided a limited explanation of why some of the employees working in the same environment as other employees suffered a single-injury event, while other employees experienced multiple-injury events. This article reports on an investigation of whether artisanal and small-scale miners in Migori County of Kenya are susceptible to a single-injury or multiple-injury incidences, and if so, what underpinning parameters explain the differences between the single incident injured and the multiple incident injured group. Mine management commitment to safety in artisanal and small-scale mining (ASM) operations is also considered. Materials and methods: The research objectives were achieved by surveying 162 uninjured and 74 injured miners. A structured, closed-end questionnaire was administered to participants after the stratification of the study population and systematic selection of the representative samples. Results: The results showed that most injured miners suffer a single-injury incident rather than experiencing multiple-injury events, and laceration (28.40%) was the common injury suffered by the miners. The analysis showed that the risk factors for the single incident injured group were not similar to those in the multiple incident injured group. The research also found mine workers have low opinion about mine management/owners commitment to safety. Conclusion: The study concluded that mine management and miners need to be educated and sensitized on the dangers of this operation. Provision of safety gears and positive safety culture must be a top priority for management.

• Korean Journal of Food Science and Technology
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• v.29 no.4
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• pp.752-757
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• 1997

Crude papain extracted at optimum condition was purified with an ethanol precipitation method. Four factors of protein recovery method were optimized by response surface methodology (RSM) and the function was expressed in terms of a quadratic polynomial equation. Adequacy of the model equation for optimum response values was tested and optimum conditions of protein recovery were 38.2 mg/mL of protein, ethanol concentration of 40% and precipitation temperature of $-8^{\circ}C$. The experimental value (68.97%) for recovery yield was closed to the predicted value (77.28%) under these conditions.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.349-356
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• 2020

This paper introduces the implementation of a driver's condition warning system using eye aspect ratio to prevent a car accident. The proposed driver's condition warning system using eye aspect ratio consists of a camera, that is required to detect eyes, the Raspberrypie that processes information on eyes from the camera, buzzer and vibrator, that are required to warn the driver. In order to detect and recognize driver's eyes, the histogram of oriented gradients and face landmark estimation based on deep-learning are used. Initially the system calculates the eye aspect ratio of the driver from 6 coordinates around the eye and then gets each eye aspect ratio values when the eyes are opened and closed. These two different eye aspect ratio values are used to calculate the threshold value that is necessary to determine the eye state. Because the threshold value is adaptively determined according to the driver's eye aspect ratio, the system can use the optimal threshold value to determine the driver's condition. In addition, the system synthesizes an input image from the gray-scaled and LAB model images to operate in low lighting conditions.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.2
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• pp.185-190
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• 2009

In this paper, an observer-based intelligent controller for the nonlinear networked control systems with packet loss is proposed for wireless sensor network. For the intelligent control of the nonlinear system, it uses the fuzzy system with Takagi-Sugeno (T-S) fuzzy model. The observer is designed for the fuzzy networked control system, and the output feedback controller is proposed for the stability of estimates and errors. The stability condition of the closed-loop system with the proposed controller is represented to the linear matrix inequality (LMI) form, and the observer and control gain are obtained by LMI. An example is given to show the verification discussed throughout the paper.

• The Transactions of the Korea Information Processing Society
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• v.4 no.2
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• pp.628-638
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• 1997

This paper describes an implementation of fault simulator that can switch level fault models such as transistor stuck-open and stuck-closed faults as well as stuck-at faults. It overcomes the limitation when only stuck-at faults are used in VLSI circuits. Signal flow of a transistor switch is bidirectional in its nature, but most of signal flows in a switch level circuits, about 95%, are in one direction. This fault simulator focuses on the way which changes a switch level circuit into a graph model with two directed edges. Two paths from Vdd to ground and from ground to directions. Logic simulation is performed along dominant signal flows. The switch level fault simulation estimates the dominant path by injecting switch-level fualts, and pattern vectors are used for faults simulation. Experimental results are shown to demonstrate correctness of the fault simulator.