• Journal of the Korea Convergence Society
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• v.9 no.3
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• pp.131-135
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• 2018

The purpose of the present study was to examine the effects of full immersion virtual reality (VR) on the autonomic nervous system. The study was conducted with 17 men in their 20s. The subjects were given full immersion VR content, and electrocardiogram (ECG) signals were measured for five minutes before and after the application of the full immersion VR. The autonomic nervous system was evaluated by analyzing the LF, HF, TP, and LF/HF ratio of the ECG signal. The obtained data was analyzed by conducting a paired sample t-test. After applying full immersion VR, the subjects' HF and TP decreased significantly, while their LF/HF ratio increased significantly. According to the results of this study, Full immersion VR provided stress to the autonomic nervous system, but the changes were within the normal range of healthy adults. Therefore, full immersion VR can be safely applied to healthy adults.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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• pp.380-391
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• 2014

In this study, the scale effect on the performance of the podded propeller of tractor type is investigated. Turbulent flow computations are carried out for Reynolds numbers increasing progressively from model scale to full scale using the CFD analysis. The result of the flow calculation for model scale Reynolds numbers agrees well with that of the experiment of a large cavitation tunnel. The existing numerical analysis indicates that the performance of the podded propeller blades is mainly influenced by the advance coefficient and relatively little by the Reynolds number. However, the drag of pod housing with propeller in operation is different from that of pod housing without propeller due to the acceleration and swirl of propeller slipstream which is altered by propeller loading as well as the pressure recovery and friction according to Reynolds number, which suggests that the pod housing drag under the condition of propeller in operation is the key factor of the scale effect on the performance between model and full scale podded propellers. The so called 'drag ratio', which is the ratio of pod housing drag to total thrust of podded propeller, increases as the advance coefficient increases due to accelerated flow in the slipstream of the podded propeller. However, the increasing rate of the drag ratio reduces continuously as the Reynolds number increases from model to full scale progressively. The contribution of hydrodynamic forces, which acts on the parts composed of the pod housing with propeller operating in various loading conditions, to the thrust and the torque of the total propeller unit are presented for a range of Reynolds numbers from model to full scales.

• Journal of the Korean Society of Radiology
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• v.8 no.4
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• pp.147-153
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• 2014

We tried to assessment about characteristics of image through quantitative evaluation method and qualitative evaluation method in Full Field Digital Mammography. It satisfied an approval standard of ten score regardless of compression ratio measuring detection score after compressing and appling an algorithm of JPEG2000 orJPEG compression targeting ACR accreditation phantom. Also, it was apparent that when we selected and compressed the image of real fine lesion and measured a change of diagnosis ability magnifing over 50 percent after compressing over 20:1 ratio, it had a strong influence on diagnosis ability. We realized that the difference between the original image according to compression ratio measuring a quantitative evaluation which is PSNR,RMSE,MAE and SSIM was relatively allowable.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.777-780
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• 2003

In this paper, an improved full wave mode ZVT-PWM DC-DC Converter is presented to maximize the regeneration ratio of resonant energy by only putting an additional diode in series with auxiliary switch. The operation of auxiliary switch in a half wave mode makes possible the soft switching condition of all switches. Furthermore, the increase of the regeneration ratio to resonant energy results in low conduction losses and minimum voltage and current stresses. The operation principles of the proposed converters are analyzed using the PWM boost converter topology as an example. Theoretically analysis and experimental results verify the validity of the boost converter topology with the proposed full wave mode ZVT-PWM converters

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.283-288
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• 2000

This paper proposes a novel Pulse Width Modulation (PWM) method for microprocessor implementation of full-bridge PWM inverters. In the method, the period of unipolar full-bridge inverters is divided equally into the frequency modulation ratio and the reference fundamental amplitude and the inverter output fundamental amplitude are compared. Using this method, the turn-on time computation of each interval is very favored for the microprocessor implementation. The harmonic analysis shows that the harmonics can be ignored when the modulation ratio is enough large. The simulation and experimental results show the effectiveness of the proposed algorithms.

• Journal of the Korean Society for Library and Information Science
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• v.32 no.1
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• pp.129-154
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• 1998

In these days the online full-text database are increasing, but conventional full-text information retrieval system has been proved with high recall ratio and low precision ratio. One of the disadvantages of full-text IR system is that it is not designed to reflect the user's information need it is due to the fact that full-text IR system has been designed based on physical and logical structure of document without considering the content of document. Therefore, the purpose of the study examined feasibility of document content structure in full-text IR system by resolving such disadvantages of conventional system. 180 Journal articles have been analyzed to find common structure of document content and finally general model of the structure of journal articles were developed. The result shows that have relation to between user's cogntive schema structure, user's information need and contents structure of document. Thus it is concluded that full-text IR system need to be designed by using document content structure in order to meet user's information need more effectively.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.1
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• pp.44-50
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• 2007

Diesel engines have high thermal efficiency, and they have less CO & HC emissions than another engines. while NOx & Soot emissions are very much. compared with exhaust emission standards. However, the limit level is more and more strengthened yearly due to the importance of environmental protection. So, the optimal countermeasures for the reduction of NOx & Soot emissions below limit level are required. Therefore. the author has investigated the effects of emulsified fuel on the characteristics of exhaust emissions. using an four-cycle, four-cylinder and direct injection diesel engine because the using of emulsified fuel among various methods for reducing NOx & Soot emissions is simple in installation low in cost and high in efficiency. The results of investigation according to various operating conditions are as follows : 1) Specific fuel consumption increase maximum 19.8% at low load. but is not affected at full load. 2) In case of emulsion ratio 25%, NOx emission decrease 32% at 75% load. 30% at full load. 3) In case of emulsion ratio 25%, Soot emission decrease 84% at 75% load, 59% at full load.

• Corrosion Science and Technology
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• v.21 no.4
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• pp.314-324
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• 2022

The objective of this investigation was to indentify major factors affecting surface roughness among various parameters of electropolishing process using the design of an experiment method (full factorial design) for UNS S31603. Factors selected included electrolyte composition ratio, applied current density, and electrolytic polishing time. They were compared through analysis of variance (ANOVA). Results of ANOVA revealed that all parameters could affect surface roughness, with the influence of electrolyte composition ratio being the highest. As a result of surface analysis after electropolishing, the specimen with the deepest surface damage was about 35 times greater than the condition with the smallest surface damage. The largest value of surface roughness after electropolishing was higher than that of mechanical polishing due to excessive processing. On the other hand, the smallest value of surface roughness after electropolishing was 0.159 ㎛, which was improved by more than 80% compared to the previous mechanical polishing. Taken all results together, it is the most appropriate to perform electrolytic polishing with a sulfuric acid and phosphoric acid ratio of 3:7, an applied current density of 300 mA/cm², and anelectrolytic polishing time of 5 minutes.

• Korean Journal of Agricultural Science
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• v.37 no.3
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• pp.501-508
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• 2010

A swirl chamber type diesel engine attachable to 18 kW agricultural tractors was improved to reduce exhaust emissions. Compression ratio and throat area ratio of the combustion chamber were varied to determine optimum combustion conditions. Tests were composed of full load and 8-mode emission tests. Compression ratio was fixed as 21, but the swirl chamber volume was increased by 3.8%. Output power, torque, specific fuel consumption, exhaust gas temperature, and smoke level were not considerably different for compression ratios of 21.5 (reference condition) and 21 (test condition), while NOx, HC, CO and PM levels for the compression ratio of 21 were decreased by 11%, 46%, 28%, 11%, respectively, from those for the compression ratio of 21.5. The tests were also conducted with a compression ratio of 22 and 4.3% increased chamber volume. Output power, torque, exhaust gas temperature and smoke level were greater, while specific fuel consumption was less for the compression ratio of 22 than those for the compression ratio of 21.5. Increase of compression ratio decreased HC and CO levels by 24%, 39%, but increased NOx and PM levels by 24%, 39%. Based on these results, a compression ratio of 21 was selected as an optimum value. Then, full load tests with the selected compression ratio of 21 were carried out for different throat ratios of 1.0%, 1.1%, 1.2%. Output power and torque were greatest and smoke was lowest when throat area ratio was 1.1%, which satisfied the target values of specific fuel consumption (less than 272 g/$kW{\cdot}h$) and exhaust gas temperature (less than $550^{\circ}C$). Therefore, a throat area ratio of 1.1% was selected as an optimum value.

• ETRI Journal
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• v.42 no.1
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• pp.17-25
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• 2020

Multiple-input multiple-output systems can achieve a full sum rate (SR) via full duplex (FD). However, its performance is degraded by self-interference (SI) that occurs between the transmitter and receiver at the same node and thus is constrained by error floors. Conversely, half duplex (HD) can avoid the SI albeit at lower spectral efficiency, and the slope of its error curve is determined by the diversity order. In this study, a link selection scheme based on switching between FD and HD is examined as a simple method to improve the bit error rate (BER) performance of FD systems. In the proposed link selection algorithm, either FD or HD is selected based on the received minimum distance and signal-to-interference plus noise ratio. Simulation results indicate that the proposed hybrid FD/HD switching system offers significant BER performance improvement when compared with that of the conventional FD and FD based on only the received minimum distance under the same fixed SR. Under relatively sufficient SI cancellation, it is demonstrated to outperform the HD with a diversity advantage in low and medium signal-to-noise ratio region.