• 대한후두음성언어의학회지
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• 제16권1호
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• pp.28-32
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• 2005

Background and Objectives : The most important two factors of the voice production are the respiratory function which is the power source of voice and the glottic closure that transform the air flow into sound signals. The purpose of this study was to investigate the differences between trained singers and untrained controls under varying intensity at a constant vocal pitch by simulataneous using the airway interruption method and electroglottography(EGG). Materials and Methods : Under two different intensity condition at a constant vocal pitch(/G/), 20(Male 10, Female 10) trained singers were studied. Mean flow rate(MFR), subglottic pressure(Psub) and intensity were measured with aerodynamic test using the Phonatory function analyzer. Closed quotients(CQ), jitter and shimmer were also investigated by electroglottography using Lx speech studio. These data were compared with that of normal controls. Results : MFR and Psub were increased on high intensity condition in all subject groups but there was no statistically significance. Statistically significant increasing of CQ. were observed in male trained singers on high intensity condition (untrained male : 51.31${\pm}$3.70%, trained male :55.52${\pm}$6.07%, p=.039). Shimmer percent, one of the phonatory stability parameters, was also decreased statistically in all subject groups(p<.001). Conclusion : The trained singers' phonation was more efficient than untrained singers. The result means that the trained singers can increase the loudness with little changing of mean flow rate, subglottic pressure but more increasing of glottic closed quotients.

• 대한기계학회논문집B
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• 제25권5호
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• pp.722-730
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• 2001

The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.

• 대한후두음성언어의학회지
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• 제12권1호
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• pp.39-45
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• 2001

Background and Objectives : A post-pubescent male classical singer has lower vocal register than a female classical singer. Countertenors who can produce higher vocal register like female classical singers with their falsetto voice and head resonance are recently active. The general purpose of this study is to analyze voice of countertenors and to determine the differences with those of classical singers. Materials and Methods : Four countertenors in Korea were examined using a videostrobos-copy and their voice were analyzed using aerodynamic, acoustic and voice range profile methods. Results and Conclusion : Countertenors could produce elevated fundamental frequency, voice intensity and mean air flow rate using large pulmonary capacity and head voiced falsetto. It means the presence of greater energy in countertenor is due to the more efficient conversion of the air flow to acoustic energy. But, they had unstable amplitude perturbation per each vocal cycle. The results indicated that countertenor is the acoustic products of different laryngeal mechanism with other classical register and it can be recognized as one of the registers of male classical singers.

• 대한후두음성언어의학회지
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• 제10권1호
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• pp.5-11
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• 1999

최근 음성장애에 관한 관심이 높아지면서 성대질환 내지는 후두질환의 정확한 진단을 위한 발성기능의 측정이 더욱 중요시되기에 이르렀다 이에 본 연구에서는 정상 한국인 남자 81명, 여자 76명과 성대용종 환자 남자 78명, 여자 65명을 대상으로 공기역학적 검사 중 컴퓨터화된 측정기구와 기류저지법으로 최대발성지속시간, 발성기류량, 평균호기류율, 및 성문하압을 연령별 및 성별에 따라 평균치를 측정, 이를 비교 분석하였다. 최대발성지속시간은 정상인 남자가 20.6${\pm}$6.34초, 여자가 17.2${\pm}$4.20초였고, 성대용종 환자에서 남자가 13.1${\pm}$4.26초, 여자가 11.6${\pm}$4.43초였다. 평균호기류율은 정상인 남자가 170.0${\pm}$67.00ml/sec, 여자가 131.1${\pm}$49.03ml/sec였고, 성대용종 환자에서 남자가 255.7${\pm}$216.52ml/sec, 여자가 183.24${\pm}$107.16ml/sec였다. 발성기류량은 정상인 남자가 3179.0${\pm}$648.94ml. 여자가 2144.1${\pm}$650.81ml였고, 성대용종 환자에서 남자가 2905.8${\pm}$1295.35ml, 여자가 1904.4${\pm}$1068.59ml였다 성문하압은 정상인 남자가 4.0${\pm}$1.88cm$H_2O$, 여자가 3.5${\pm}$4.20cm$H_2O$였고, 성대용종 환자에서 남자가 4.2$\pm$1.48cm$H_2O$, 여자가 3.9${\pm}$1.12cm$H_2O$였다. 성대용종 환자에서 통계학적으로 유의성있게 최대발성지속시간은 감소하고, 평균호기류율은 증가하였으며, 발성기류량과 성문하압은 여자환자에서만 의미 있게 각각 감소하거나 증가하였다. 이상의 결과는 정상인과 성대용종 환자에 있어서 객관적인 공기역학적 검사결과를 보여주며 이는 성대용종 환자의 음성이상에 대한 상태판정이나 치료 후 효과 판정에 기본자료로 이용할 수 있을 것으로 생각된다.

• 연구논문집
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• 통권29호
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• pp.5-15
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• 1999

Present study deals with performance analysis of an inert gas generator (IGG) which is to be used as an effective mean to suppress the fire. The IGG uses a turbo jet cycle gas turbine engine to generate inert gas for fire extinguishing. It is generally known that a lesser degree of oxygen content in the product of combustion will increase the effectiveness of fire suppressing. An inert gas generator system with water injection will bring advantages of suffocating and cooling effects which are considered as vital factors for fire extinguishing. As the inert gas is injected to the burning site, it lowers the oxygen content of the air surrounding the flame as well as reduces the temperature around the fire as the vapour in the inert gas evaporates during the time of spreading. Some important aspects of influencing parameters, such as, air excess coefficient. $\alpha$, compressor pressure ratio, $ pi_c$, air temperature before combustion chamber, $T_2$, gas temperature after combustion chamber, $T_3$, mass flow rate of water injection, $M_w$, etc., on the performance of IGG system are investigated. Calculations of total amount of water needed to reduce the turbine exit temperature to pre-set nozzle exit temperature employing a heat exchanger were made to compare the economics of the system. A heat exchanger with two step cooling by water and steam is considered to be better than water cooling only. Computer programs were developed to perform the cycle analysis of the IGG system and heat exchanger considered in the present study.

• 설비공학논문집
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• 제28권2호
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• pp.75-80
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• 2016

There are three types of dehumidification systems : refrigeration dehumidification method, desiccant dehumidification method and hybrid dehumidification method. The first method involves removing moisture by condensation below the dew point, the second method involves absorption by a desiccant material and the last is an integration method. However, the refrigeration dehumidification system consumes too much power and controlling the humidity ratio is difficult. The desiccant dehumidification system uses less power but it has problems of environmental pollution. The hybrid dehumidification system has the disadvantage of a high initial cost. On the other hand, the energy consumption of the membrane based dehumidification system is lower than for the refrigeration dehumidification system. Also, it is an environmentally friendly technology. In this study, the performance parameters are evaluated for the dehumidification system using a hollow fiber membrane. Available area, duct side dry-bulb temperature, sweep gas flux (flow rate) and LMPD (Log Mean Pressure Difference) were used as the performance parameters.

• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1775-1783
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• 2003

The method of flame hole dynamics is demonstrated as a mean to simulate turbulent flame extinction. The core of the flame hole dynamics involves derivation of a random walk mapping for the flame holes, created by local quenching, between burning and quenched states provided that the dynamic characteristics of flame edges is known. Then, the random walk mapping is projected to a background turbulent field. The numerical simulations are carried out with further simplifications of flame string and unconditioned scalar dissipation rate. The simulation results show how the chance of partial quenching is influenced by the crossover scalar dissipation rate. Finally, a list of improvements, necessary to achieve more realistic turbulent flame quenching simulation, are discussed.

• 동력기계공학회지
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• 제5권2호
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• pp.22-29
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• 2001

This paper represents axial mean velocity, turbulent kinetic energy and swirl number based on momentum flux measured in the X-Y plane and Y-Z plane respectively of a cone type gas swirl burner by using X-probe from the hot-wire anemometer system. This experiment is carried out at flow rates 350 and $450{\ell}/min$ respectively, which are equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of a subsonic wind tunnel. Axial mean velocities and turbulent kinetic energies show that their maximum values exist centering around narrow slits situated radially on the edge of and in the forefront of a burner until $X/R{\fallingdotseq}1.5$, but they have a peculiar shape like a starfish diffusing and developing into inward and outward of a burner by means of the mixing between flows ejected from narrow slits, an inclination baffle plate and swirl vanes respectively according to downstream regions. Moreover, they show a relatively large value in the inner region of 0.5$S_m$ obtained by integration of velocity profiles shows a characteristic that has an inflection point composing of the maximum and minimum value until X/R<3, but shows close agreement with the geometric swirl number after a distance of X/R=3.

• 한국환경보건학회지
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• 제30권2호
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• pp.140-148
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• 2004

To evaluate the acute effects of fine particles on pulmonary function, a longitudinal study was conducted. This study was carried out for the schoolchildren (3rd and 6th grades) living in Beijing, China. Each child was provided with a mini-Wright peak flow meter and a preformatted health symptom diary for 40 days, and was trained on their proper use. Participants were instructed to perform the peak flow test three times in standing position, three times a day (9 am, 12 pm, and 8 pm), and to record all the readings along with the symptoms (cold, cough, and asthmatic symptoms) experienced on that day. Daily measurement of fine particles (PM$_{10}$ and PM$_{2.5}$) was obtained in the comer of the playground of the participating elementary school for the same period of this longitudinal study. The relationship between daily peak expiratory flow rate (PEFR) and fine particle levels was analyzed using a mixed linear regression models including gender, height, the presence of respiratory symptoms, and daily average temperature and relative humidity as extraneous variables. The total number of students participating in this longitudinal study was 87. The range of daily measured PEFR was 253-501$\ell$/min. In general, the PEFR measured in the morning was lower than the PEFR measured in the evening (or afternoon) on the same day. The daily mean concentrations of PM$_{10}$ and PM$_{2.5}$ over the study period were 180.2$\mu\textrm{g}$/㎥ and 103.2$\mu\textrm{g}$/㎥, respectively. The IQR (inter-quartile range) of PM$_{10}$ and PM$_{2.5}$ were 91.8$\mu\textrm{g}$/㎥ and 58.0$\mu\textrm{g}$/㎥. During the study period, the national ambient air quality standard of 150$\mu\textrm{g}$/㎥ (for PM$_{10}$) was exceeded in 23 days (57.5%). The analysis showed that an increase of 1$\mu\textrm{g}$/㎥ of PM$_{10}$ corresponded to 0.59$\mu\textrm{g}$/㎥ increment of PM$_{2.5}$. Daily mean PEFR was regressed with the 24-hour average PM$_{10}$ (or PM$_{2.5}$) levels, weather information such as air temperature and relative humidity, and individual characteristics including gender, height, and respiratory symptoms. The analysis showed that the increase of fine particle concentrations was negatively associated with the variability in PEFR. The IQR increments of PM$_{10}$ or PM$_{2.5}$ (at 1-day time lag) were also shown to be related with 1.54 $\ell$/min (95% Confidence intervals: 0.94-2.14) and 1.56$\ell$/min (95% CI: 0.95-2.16) decline in PEFR.R.ine in PEFR.ine in PEFR.

• 한국자동차공학회논문집
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• 제14권1호
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• pp.92-99
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• 2006

The swirl ratio of a charge in the cylinder was estimated by calculating the ratio of the rotary speed of charge which could be simulated from the rotary speed of paddle in the swirl measurement apparatus, to the engine speed which could be calculated by measuring intake air flow rate. The automation of the swirl ratio measurement for cylinder head was achieved by controling both valve lift in cylinder head and a suction pressure of surge tank using two step-motors. The number of measurement position for calculating mean swirl ratio was varied by adjusting the interval of valve lift. The mean swirl ratio with varying the number of measurement position showed nearly constant value. Two measurement methods for measuring the swirl ratio were compared, one was to control the suction pressure of the surge tank with PID (proportional, integral, differential) mode with by-pass valve controlled by the step motor and the other did not control the surge tank pressure by fixing the by-pass valve. The difference of the mean swirl ratio between the two measurement methods showed nearly constant value with varying the number of measurement position. This means that the w/o PID control method could be preferred to the PID control method which has been used, due to the simpleness of the swirl measurement.