• Proceedings of KOSOMES biannual meeting
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• 2017.04a
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• pp.125-125
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• 2017

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.318-320
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• 2007

Single-phase cycloconverters are widely used for ac-ac power conversion especially for speed control of ac drives. In this paper, a new single-phase to single-phase Z-source cycloconverter topology is proposed. The proposed single-phase Z-source cycloconverter can boost to a desired voltage with various frequency. Thus, it is called a frequency step-down and amplitude voltage step-up converter. The operating principle of the proposed topology is presented. Analysis and simulation for this single-phase Z-source cycloconverter are also presented.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.85-92
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• 2004

As a research to develop a SCRAM jet engine is actively conducted, a necessity to produce a high-enthalpy flow in a laboratory is increasing. In order to develop the SCRAM-jet engine, stabilized combustion in a supersonic flow-field should be attained, in which a duration time of flow is extremely short. Therefore, a mixing process of breathed air and fuel, which is injected into supersonic flow-fields is one of the most important problem. Since, the flow inside SCRAM jet engine has high-enthalpy, an experimental facility is required to produce such high-enthalpy flow-field. In this study, a detonation-driven shock tunnel was built and was used to produce high-enthalpy flow. Further-more, SCRAM jet engine model equipped backward-facing step was installed at test section and flow-fields were visualized using color-schlieren technique and high speed video camera. The fuel was injected perpendicular to the flow of Mach number three behind backward-facing step. The height of the step, distance of injection and injection pressure were changed to investigate the effects of step on a mixing characteristic between air and fuel. The schlieren photograph and pressure histories show that the fuel was ignited behind the step.

• Journal of Sensor Science and Technology
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• v.28 no.4
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• pp.251-255
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• 2019

We propose a two-step lithography process to minimize edge-bead issues caused by thick photoresist (PR) coating. In the conventional PR process, the edge bead can be efficiently removed by applying an edge-bead removal (EBR) process while rotating the silicon wafer at a high speed. However, applying conventional EBR to the production of desired PR mold with unique negative patterns cannot be used because a lower rpm of spin coating and a lower temperature in the soft bake process are required. To overcome this problem, a two-step lithography process was developed in this study and applied to the fabrication of a polydimethylsiloxane (PDMS) film having super-hydrophobic characteristics. Following UV exposure with a first photomask, the exposed part of the silicon wafer was selectively removed by applying a PR developer while rotating at a low rpm. Then, unique PR mold structures were prepared by employing an additional under-exposure process with a second mask, and the mold patterns were transferred to the PDMS. Results showed that the fabricated PDMS film based on the two-step lithography process reduced the height difference from 23% to 5%. In addition, the water contact angle was greatly improved by spraying of hydrophobic nanosilica on the dual-scaled PDMS surface.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.392-399
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• 2009

The paper concerns the description of the step by step development process of the new fixed blade runner called "Mixer" suitable for the uprating of the Francis turbines units installed at the older low head hydropower plants. In the paper the details of hydraulic and mechanical design are presented. Since the rotational speed of the new runner is significantly higher then the rotational speed of the original Francis one, the direct coupling of the turbine to the generator can be applied. The maximum efficiency at prescribed operational point was reached by the geometry optimization of two most important components. In the first step the optimization of the draft tube geometry was carried out. The condition for the draft tube geometry optimization was to design the new geometry of the draft tube within the original bad draft tube shape without any extensive civil works. The runner blade geometry optimization was carried out on the runner coupled with the draft tube domain. The blade geometry of the runner was optimized using automatic direct search optimization procedure. The method used for the objective function minimum search is a kind of the Nelder-Mead simplex method. The objective function concerns efficiency, required net head and cavitation features. After successful hydraulic design the modal and stress analysis was carried out on the prototype scale runner. The static pressure distribution from flow simulation was used as a load condition. The modal analysis in air and in water was carried out and the results were compared. The final runner was manufactured in model scale and it is going to be tested in hydraulic laboratory. Since the turbine with the fixed blade runner does not allow double regulation like in case of full Kaplan turbine, it can be profitably used mainly at power plants with smaller changes of operational conditions or in case with more units installed. The advantages are simple manufacturing, installation and therefore lower expenses and short delivery time for turbine uprating.

• Journal of the Korean Society of Physical Medicine
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• v.12 no.2
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• pp.75-82
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• 2017

PURPOSE: The purpose of this study was to determine the effects of arm training in standing position on balance and walking ability in chronic stroke patients. METHODS: Sixteen chronic stroke patients were allocated equally and randomly to an experimental group (n=8) or a control group (n=8). All participants received 60 minutes of comprehensive rehabilitation treatment, the experimental group additionally received an arm training in standing position for 30 minutes, while the control group additionally performed a treadmill training for 30 minutes. These 30-minute training sessions were held three times per week for six weeks. Upper extremity function was assessed using Fugle-Meyer motor assessment function upper extremity (FMA-UE), balance was assessed using Berg balance scale (BBS), and walking ability (gait speed, cadence, step length, and double limb support period) was assessed using the GAITRite system. RESULTS: Improvement on all outcome measures was identified from pre-to-post intervention for both groups (p<.05). Post-intervention, there was a significant between-group difference on BBS, gait speed, cadence, step length, and double limp support period (p<.05). The experimental group exhibited greater improvement in the BBS (p=.01; z=-2.48), gait speed (p=.01; z=-3.26), cadence (p=.02; z=-2.31), step length (p=.01; z=-3.36), and double limb support period (p=.03; z=-2.84) compared to the control group. CONCLUSION: The findings of this study suggest that arm training in standing position may be beneficial for improving balance and walking ability of patients with chronic stroke.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.3
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• pp.158-163
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• 2009

LMS(Least Mean Square) algorithm requires simple equation and is used widely because of the low complexity. If the convergence speed increase, LMS algorithm has a divergence in case of sharp environment changes. And if a stability increase, the convergence speed becomes slow. This algorithm based on a trade off between fast convergence and system stability. To improve this problem, VSSLMS (Variable Step Size LMS) algorithm was developed. The VSSLMS algorithm improved the convergence speed and performance as adjusting step size using error signal. In this paper, I-VSSLMS algorithm is proposed tor improve the performance of adaptive noise canceller in real-time environments. The proposed algorithm is applied to adaptive noise canceller using TMS320C6713 DSP board and we did simulation by real time. Then we compared performance of each algorithm and demonstrated that proposed algorithm has superior performance.

• PNF and Movement
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• v.17 no.1
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• pp.47-56
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• 2019

Purpose: This study investigated the effects of neck pattern of proprioceptive neuromuscular facilitation (PNF) on balance and walking ability in patients with chronic stroke. Methods: Fourteen participants with chronic stroke were randomly assigned to vestibular rehabilitation and then divided into two groups: the neck pattern group or treadmill group. Each group underwent 20 sessions (20 minutes/day, five days/week, for four weeks). Patients were assessed with the Berg balance scale (BBS) and gait parameters (gait speed, cadence, step length, and double-limb support period) using a GAITRite system. Results: Vestibular rehabilitation for the neck pattern group and the treadmill group showed significant intragroup improvement on the BBS and in terms of gait speed, cadence, step length, and double-limb support period (p < 0.05). Vestibular rehabilitation was more effective for the neck pattern group than for the treadmill group in terms of the BBS (p = 0.00; 95% CI, 1.49-5.94), gait speed (p = 0.01; 95% CI, 0.05-0.16), cadence (p = 0.02; 95% CI, 0.54-4.99), and step length (p = 0.00, 95% CI, 1.55-4.62). Conclusion: This study used the neck pattern of PNF for vestibular rehabilitation in patients with chronic stroke. The results showed significant improvement in the patients' balance and walking ability. Therefore, the neck pattern of PNF for vestibular stimulation may be more effective than treadmill training to improve balance and walking ability in patients with chronic stroke.

• Design & Manufacturing
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• v.17 no.4
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• pp.72-78
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• 2023

Injection molding is a process widely used in various industries because of its high production speed and ease of mass production during the plastic manufacturing process, and the product is molded by injecting molten plastic into the mold at high speed and pressure. Since process conditions such as resin and mold temperature mutually affect the process and the quality of the molded product, it is difficult to accurately predict quality through mathematical or statistical methods. Recently, studies to predict the quality of injection molded products by applying artificial neural networks, which are known to be very useful for analyzing nonlinear types of problems, are actively underway. In this study, structural optimization of neural networks was conducted by applying multi-task learning techniques according to the characteristics of the input and output parameters of the artificial neural network. A structure reflecting the characteristics of each process step was applied to the input parameters, and a structure reflecting the quality characteristics of the injection molded part was applied to the output parameters using multi-tasking learning. Building an artificial neural network to predict the three qualities (mass, diameter, height) of injection-molded product under six process conditions (melt temperature, mold temperature, injection speed, packing pressure, pacing time, cooling time) and comparing its performance with the existing neural network, we observed enhancements in prediction accuracy for mass, diameter, and height by approximately 69.38%, 24.87%, and 39.87%, respectively.

• Journal of the Korea Society of Computer and Information
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• v.29 no.5
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• pp.123-129
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• 2024

CPR is very important to paramedics, but the chest compression performed while on the move main stretcher is less accurate. The purpose of this study is to find out the difference between performing chest compression on the side of the main stretcher using C-step and on the patient's over the belly in order to increase the effect of CPR on the main object while on the move. As a result of the study, the appropriate depth (t=4.132, p=.000) and speed (t=7.177, p=.000) were shown in the group to which the C-step was applied, and the accuracy was higher (t=6.774, p=.000). In addition, it was found that there were few location defects (t=-5.197, p=.000) and too shallow errors (t=-2.948, p=.008) in the group to which the C-step was applied. In conclusion, mounting a C-step on the main stretcher seems to help improve the quality of chest compression, and it is thought that this will increase the efficiency of chest compression.