• Journal of the Korean Society of Combustion
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• v.8 no.3
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• pp.31-37
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• 2003

The objective of this work is to investigate the effect of swirl, injection pressure and pilot injection on D.I.Diesel combustion by using a transparent engine system. The test engine is equipped with common rail injection system to obtain high pressure and to control injection timing and duration. In this study, the combustion analysis and steady flow test were conducted to estimate the heat release rate from in-cylinder pressure and pilot injection was investigated by using LII technique. As the results, high injection pressure was found to shorten ignition delay as well as enhance peak pressure and heat release rate was greatly affected by injection timing and pilot injection. In addition, the results showed that the period of soot formation corresponded to the diffusion flame.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.51-58
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• 2012

Accurate transmission and estimation of the channel statistics affected by high Doppler spread is one of the main issues of concern for the latest and future mobile communication systems. Therefore, it is important to research in novel channel estimation techniques that overcome the limitations of conventional methods. In this paper, we propose a novel channel estimation method that, after a simple estimation in the first OFDM symbol, uses Kalman filter to predict the channel in the rest of OFDM symbols with pilot subcarriers. Our method is designed considering the lattice-type arrangement of pilot subcarriers in LTE-Advanced, since most of the studies so far focus on block-type or comb-type pilot arrangements. In addition, to optimize the results, we use the filtering of channel impulse response and Wiener Filter for the estimation of the channel frequency response in the rest of the subcarriers.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.3
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• pp.45-51
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• 2012

This work was investigated 2-stage injection strategy on combustion and emissions in a direct injection compression-ignition engine fueled with DME. Single cylinder engine was equipped with common rail. Injection pressure was 700bar, dSOI between the main injection and the pilot injection was varied. Diesel was used as compared fuel of DME in all cases. The results was shown that maximum pressure was higher than all cases and its amount of DME and diesel was similar. Regardless the pilot injection, the main fuel injection timing was same. The heat release rate of the main injection for diesel was high while that of pilot injection for DME was high. The THC was very low regardless of the fuel type and injection strategy. In the single injection, NOx was increased to retard of main injection timing regardless of the fuel type. NOx emissions was decreased with the retardation of the main injection timing regardless of the fuel type in the case of 2-stage injection strategy.

• Journal of Multimedia Information System
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• v.7 no.4
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• pp.249-256
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• 2020

Learning methods using various assistive and smart devices have been developed to enable independent learning of the disabled. Pointer control is the most important consideration for the disabled when controlling a device and the contents of an existing graphical user interface (GUI) environment; however, difficulties can be encountered when using a pointer, depending on the disability type; Although there are individual differences depending on the blind, low vision, and upper limb disability, problems arise in the accuracy of object selection and execution in common. A multimodal interface pilot solution is presented that enables people with various disability types to control web interactions more easily. First, we classify web interaction types using digital devices and derive essential web interactions among them. Second, to solve problems that occur when performing web interactions considering the disability type, the necessary technology according to the characteristics of each disability type is presented. Finally, a pilot solution for the multimodal interface for each disability type is proposed. We identified three disability types and developed solutions for each type. We developed a remote-control operation voice interface for blind people and a voice output interface applying the selective focusing technique for low-vision people. Finally, we developed a gaze-tracking and voice-command interface for GUI operations for people with upper-limb disability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.6
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• pp.333-342
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• 2014

The pilot assisted channel frequency response (CFR) estimation schemes for an OFDM-based system with virtual subcarriers are analyzed under the assumption that pilot symbols are located according to a comb-type pattern in the OFDM block. In particular, as the minimum mean square error (MMSE) based scheme aiming to directly predict the channel impulse response and the MMSE based scheme aiming to suppress the leakage have not been clearly compared, by proving that the mean square errors (MSEs) of the latter scheme is always larger than that of the former scheme, this paper shows that the former scheme is superior to the latter scheme. Moreover, the impact of the number of pilots on the performances of the MMSE and least-square based channel estimation schemes are investigated. The performance analyses of the presented schemes are confirmed by computer simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.4
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• pp.98-107
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• 1996

In order to predict analytically torque, thrust force, tool life and chip formation in drilling, cutting models for chisel edge with various tool-chip contact length were developed in this type. Also, the experimental tests are run with various pilot holes. The following conclusions were obtained from the analysis. \circled1 It's also found experimentally that thrust force(Fz) decreases as pilot hole diameter increases. \circled2 Surface roughness for material(G) is larger that for material(J). The difference over two materials in roughness value about 0.5$mu extrm{m}$. \circled3 Flank wear of the drill in cutting material of G less than any other kinds of materials(F, G, H, I, J). \circled4 In drilling a deep hole on a workpiece over SM45C either twist drill. The chip was conical helix type at the fist suspensely change the two segment type and than two a long pitch helix style.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.112-119
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• 2009

An automatic transmission of construction equipment is controlled by hydraulic and electronic system for doing in various functions like as shifting and operation. The shifting is operated by the engaged and disengaged clutch motion from hydraulic power. On the shifting process, suitable pressure control to the clutch is required for smooth shifting. Hydraulic control system in the automatic transmission is divided by the pilot control type and the direct control type greatly. The direct control type has an advantage than the pilot control type. Because the structure is simple, the design and the manufacture are having less troubles and the system can be maximized precision pressure control. However, the excellent performance proportional control valve should be used to achieve proper control-ability. In this study, the dynamic analysis model composing the automatic transmission and hydraulic system for forklift truck is presented to simulate the characteristics of hydraulic system about the direct control type. That model is verified the validity compared the results of the testing examination. Parameters of input signal are analyzed to reduce the output torque according to input control signal is affected in shifting characteristic.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.17 no.3
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• pp.7-13
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• 2009

This study examined 1) student pilots' personality types, 2) the correlation between students' personality types and their achievement in flight training, 3) the correlation between students' personality types and Instructor Pilot(IP)s' personality type. The study used the Korean version of Myers-Briggs Type Indicator (MBTI) form. A total of 164 students in the year of 2000-2003 completed the inventory. The noticeable majority of student pilot were extroverted (59.6%) - Sensing (79.5%) - Thinking (70.2%) - Judgers (68.9%). Comparing personality types with flight achievement in showed no significant correlation. There was, however, a significant difference seen in comparing personality types with students' flight achievements. Thinking-type students showed higher flight achievements than feeling-type, and some of the personality types combination affects trainee's flight achievement. When both student and the Instructor have same attitude such as E-E or I-I, student's flight achievement was higher than when they have opposite attitude of personality. these findings implicate that the cooperation of students' and IP's personality could affect the students' flight achievement.

• International Journal of Automotive Technology
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• v.6 no.4
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• pp.315-322
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• 2005

This work was performed to investigate the effect of a split injection on spray characteristics of fuel sprays injected from a common rail system. In order to analyze the spray behavior and atomization characteristics at various rates of split injections, the injection durations of pilot and main injections were varied in experiments. The injection rate of split injection was measured to study the effect of the pilot injection on the main injection. By using a Nd:YAG laser and an ICCD camera, the development of the injected spray was visualized at various elapsed time from the start of injection. The microscopic characteristics such as SMD and axial velocity were analyzed by using a phase Doppler particle analyzer system. The results indicate that the ambient gas flow generated by the pilot injection affects the behavior of main spray, whereas the effect of pressure variation on the main spray is little. The spray tip penetration of a main spray with pilot injection is longer than that of the single injection by the effect of ambient gas flow. Also the main spray produces larger droplets than the pilot spray due to a small relative velocity between the droplets and ambient gas.

• Restorative Dentistry and Endodontics
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• v.49 no.1
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• pp.3.1-3.8
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• 2024

This article is a narrative review that discusses the recommended sample size requirements to design a pilot study to assess the reliability of a questionnaire. A list of various sample size tables that are based on the kappa agreement test, intra-class correlation test and Cronbach's alpha test has been compiled together. For all calculations, type I error (alpha) was set at a maximum value of 0.05, and power was set at a minimum value of 80.0%. For the kappa agreement test, intra-class correlation test, and Cronbach's alpha test, the recommended minimum sample size requirement based on the ideal effect sizes shall be at least 15, 22, and 24 subjects respectively. By making allowances for a non-response rate of 20.0%, a minimum sample size of 30 respondents will be sufficient to assess the reliability of the questionnaire. The clear guideline of minimum sample size requirement for the pilot study to assess the reliability of a questionnaire is discussed and this will ease researchers in preparation for the pilot study. This study provides justification for a minimum requirement of a sample size of 30 respondents specifically to test the reliability of a questionnaire.