• Journal of the Korean Institute of Navigation
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• v.23 no.3
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• pp.35-44
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• 1999

This research aims to seek active control of ball-beam position stability by resorting to neural networks whose layers are given bias weights. The controller consists of an LQR (linear quadratic regulator) controller and a neural networks controller in parallel. The latter is used to improve the responses of the established LQR control system, especially when controlling the system with nonlinear factors or modelling errors. For the learning of this control system, the feedback-error learning algorithm is utilized here. While the neural networks controller learns repetitive trajectories on line, feedback errors are back-propagated through neural networks. Convergence is made when the neural networks controller reversely learns and controls the plant. The goals of teaming are to expand the working range of the adaptive control system and to bridge errors owing to nonlinearity by adjusting parameters against the external disturbances and change of the nonlinear plant. The motion equation of the ball-beam system is derived from Newton's law. As the system is strongly nonlinear, lots of researchers have depended on classical systems to control it. Its applications of position control are seen in planes, ships, automobiles and so on. However, the research based on artificial control is quite recent. The current paper compares and analyzes simulation results by way of the LQR controller and the neural network controller in order to prove the efficiency of the neural networks control algorithm against any nonlinear system.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.4
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• pp.153-158
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• 2017

When considering the proper function and life cycle length of a product, its surface finish plays an important role. This experimental study was carried out to understand the effect of input factors on surface roughness and how it can be minimized by controlling the input parameters. This experimental work was performed by machining the surface of STD 61 blocks with a surface inclined at $30^{\circ}$ by ball end-milling and optimizing the input parameters using the Taguchi technique. Signal-to-Noise (S/N) ratio and analysis of variance (ANOVA) were applied to find the significance of the input parameters. The optimum level of input parameters to minimize surface roughness was obtained.

• Journal of the Korean Chemical Society
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• v.6 no.1
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• pp.32-35
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• 1962

Six frogs (Rana nigromaculata 25∼40 gm) were adapted to light for 2 hours. Then 0.02 ml of 3% nicotinamide and 0.02 ml of 0.6% folic acid were injected into the vitreous body of the right eye-ball, and 0.02 ml normal saline solution into the vitreous body of the left eye-ball respectively. After dark adaptation for an hour-their heads were cut off under a dim red light (650 $m{\mu}$). The retinae were removed from the left eye-ball for the control group and from the right for the test group respectively. Then rhodopsin was extracted from the retinae with 3 ml of 2% digitonin solution(pH = 7.0) for 17 hours at 0$^{\circ}C$ in the dark. The optical densities before and after the illumination of the extract were measured and compared with those of the control group. The results are as follows: 1) The group which had been injected with 0.02 ml of 3% nicotinamide solution had the promotive action on tile regeneration of rhodopsin in comparison with the control group. 2) The group which had been injected with 0.02 ml of 0.6% folic acid solution had the controlling action on the regeneration of rhodopsin in comparison with the control group.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.110-116
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• 1997

The tribological behaviour of WS$_2$ solid lubricant was investigated using a ball-on-disk type tester. The WS$_2$ powder was spray-coated at room temperature and the effects of specimen configuration, atmosphere, applied load and rotating spccd on the friction coefficient was examined. WS$_2$ coated ball and disk showed the lowest friction coefficient of 0.05 in the nitrogen atmosphere under 0.3 kgf and 100 rpm, whereas relatively high coefficient of 0.1 - 0.15 was observed in air atmosphere. This confirmed that the spray-coated WS$_2$ solid lubricant was effective in reducing the friction coefficient and improving wear life in nitrogen atmosphere.

• Journal of Powder Materials
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• v.10 no.6
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• pp.422-429
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• 2003

The reduction mechanism of the composite powders mixed with $WO_3$ and CuO has been studied by using thermogravimetry (TG), X-ray diffraction, and microstructure analyses. The composite powders were made by simple Turbula mixing, spray drying, and ball-milling in a stainless steel jar with the ball to powder ratio of 32 to 1 at 80 rpm for 1 h without process controlling agents. It is observed that all the oxide composite powders are converted to W-coated Cu composite powder after reducing treatment under hydrogen atmosphere. For the formation mechanism of W-coated Cu composite powder, the sequential reduction steps are proposed as follows: CuO contained in the ball-milled composite powder is initially reduced to Cu at the temperature range from 20$0^{\circ}C$ to 30$0^{\circ}C$. Then, $WO_3$ powder is reduced to W $O_2$ via W $O_{2.9}$ and W $O_{2.72}$ at higher temperature region. Finally, the gaseous phase of $WO_3(OH)_2$ formed by reaction of $WO_2$ with water vapour migrates to previously reduced Cu and deposits on it as W reduced by hydrogen. The proposed mechanism has been proved through the model experiment which was performed by using Cu plate and $WO_3$ powder.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.99-103
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• 1998

The curved surface machined by plate end mill causes a excess non-cutting volume, in these cases ball end mill is used for the curved surfaces. This study is aimed to obtain the optimum cutting conditions of various cutting speed, table speed, tool diameter, radius of curvature roughness on the conditions of various cutting speed, tool diameter, radius of curvature when machining the curved surface using the ball end mill. After designing curve rates, obtaining NC data by CAD/CAM system through CC-Cartesian method and transferred the data through DNC system, we machined the specimens by the CNC machining center, The surface roughness of specimens was measured by surface roughness tester and CNC 3D coordinate measuring machine. The cutting condition were the same as follow velocity; 15, 20, 25 30m/min, feed rate;40, 60, 80, 100m/min and radius of curvature; 30,40,50,60mm, tool diameters; ø8, ø12, ø16, ø 20mm. Analizing the working results, we can acquire the optimum cutting condition of curved specimen at the cutting velocity of 20~25m/min and the feed rate of 80mm/min. As the same cutting condition the best surface roughness was showed at ø16mm of the tool diameter. But the tool diameter was smaller than ø8mm. we could improve for the surface roughness by controlling the cusp.

• Physical Therapy Rehabilitation Science
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• v.9 no.1
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• pp.18-24
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• 2020

Objective: The purpose of this study was to compare the activities of the abdominal muscles according to trunk stabilization exercises using Swiss ball in normal individuals. Design: Cross-sectional study. Methods: Ten healthy university students participated in this study. The subjects were required to complete the following three exercise positions: Exercise position 1, sitting on a Swiss ball and lifting the legs; Exercise position 2, pushing to a plank position from an ending position; and Exercise position 3, push-up posture with the legs on a Swiss ball. Changes in the trunk muscle activities were estimated using Biometric electromyography (EMG). Activities of the dominant side internal oblique muscle (IOM) and external oblique muscle (EOM) were estimated in all participants. The maximal voluntary isometric contraction (MVIC %) was measured to standardize the EMG signals for the IOM and EOM during maximum resistance when sitting up with each shoulder pointing towards the contralateral pelvis with knees bent and both arms crossed on the chest for 5 seconds. Results: There was a significant difference in the activity of the internal and external oblique muscles between Exercises 1 and 2 and Exercises 1 and 3 (p<0.05). Furthermore, the IOM/EOM activity ratio was the greatest during Exercise 3 and the smallest during Exercise 1. IOM and EOM activities were the greatest during Exercise 2 with greater EOM activity. Conclusions: In future studies, it will be necessary to investigate muscle activities by supplementing the above-mentioned limitations during the stabilization exercise. The results of this study may be used as a basis for controlling the intensity and frequency of exercise while prescribing trunk stabilization exercises.

• The Journal of Korean Physical Therapy
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• v.29 no.4
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• pp.181-186
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• 2017

Purpose: The paper presents an intervention for clinical applications in the future by examining the effects of 3D stabilization exercise on patients with lumbar instability, which causes problems in the muscles and balance, and analyzing the effects of balanced lumbar muscles on the static balance. Methods: After collecting samples randomly from thirty patients with lumbar instability, fifteen patients selected for 3D stabilization exercise were placed in the stability group and fifteen patients selected for Swiss ball exercise were placed in the ball exercise group. The intervention program was applied for thirty minutes a session, once a day, three days a week for four weeks. Before the intervention, the lumbar muscle activity and static balance were measured. After four weeks, they were re-measured in the same way and the data were analyzed. Results: In relation to the within-group changes in muscle activity, all groups except for the LEO and REO groups showed significant differences. Regarding the between-group changes in muscle activity depending on the left and right difference, ES, RA, and TrA but not EO showed significant differences. In addition, there were significant differences in the between-group change in static balance. Conclusion: 3D stabilization exercise improves the muscle activity by promoting a balanced posture of lumbar muscles and changing senses, such as a proprioceptor but this had a positive influence on the static balance by controlling the balance of muscles.

• Journal of the Korean Institute of Gas
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• v.5 no.2 s.14
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• pp.62-68
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• 2001

Overpressure in pipeline attached to outlet of LPG vaporizer has been studied to provide countermeasures to prevent it. The cause of liquefaction in pipeline was reviewed using vapor pressure curve with temperature, pressure, and composition to suggest method of controlling such parameters. Performance of vaporizer has been tested to detect defective design of float ball, and then improved scheme was suggested. Trouble of regulator attached to vaporizer was also studied to give countermeasures.

• Journal of Powder Materials
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• v.18 no.4
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• pp.365-371
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• 2011

In this study, gradient porous Al-Cu sintered body was fabricated by powder metallurgy processing. Al-Cu powder mixtures were prepared by low energy ball milling with various milling time. After ball milling for 3h, the shape of powder mixtures changed to spherical type with size of 100~500 ${\mu}m$. Subsequently, Al-Cu powder mixtures were classified (under 150, 150~300 and over 300 ${\mu}m$) and compacted (20, 50 and 100 MPa). Then, they were sintered at $600^{\circ}C$ for various holding time (10, 30, 60 and 120 min) in $N_2$ atmosphere. The sintered bodies had 32~45% of porosity. As a result, the optimum holding time was determined to be 60 min at $600^{\circ}C$ and sintered bodies with various porosity were obtained by controlling the compacting pressure.