• Title/Summary/Keyword: Saturation Length

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Legislative study on the qualification of level 1 emergency medical technicians (1급 응급구조사의 자격에 대한 입법론적 고찰)

  • Hwang, Seong-Ho
    • The Korean Journal of Emergency Medical Services
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    • v.23 no.3
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    • pp.17-27
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    • 2019
  • Purpose: To provide legislative data for the amendment of Article 36 of the Emergency Medical Service Act on the qualifications of emergency medical technicians. Methods: The study was drafted based on the Emergency Medical Service Act; data on the emergency medical technicians (EMT) system and curriculum in Korea, United States. Japan, and Taiwan; and previous studies on the EMT system in Korea. Results: The length of education. work scope. amd role of level 1 EMTs vary significantly depending on the type of qualifications they have as emergency medical professionals, while the supply of level 1 EMTs has already reached a point of saturation. Accordingly, the current regulation on allowing level 2 EMTs with at least three years of experience to take the level 1 EMT test presents serious inequity for students just graduating from their emergency medical services program. It is also a factor that degrades the professionalism of level 1 EMTs. Conclusion: Article 36, paragraph 2. subparagraph 3 of the Emergency Medical Services Act pertaining to regulations on "EMTs who have worked as level 2 EMTs for at least 3 years" needs to be removed.

Flow Condensation Heat Transfer Coefficients of Pure Refrigerants (순수냉매의 흐름응축 열전달계수)

  • 김신종;송길홍;정동수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.2
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    • pp.175-183
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    • 2002
  • Flow Condensation heat transfer coefficients (HTCs) of Rl2, R22, R32, Rl23, Rl25, R134a, R142b were measured experimentally on a horizontal plain tube. The experi- mental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water-glycol loop. The test section in a refrigerant loop was made of a copper tube of 8.8 mm inner diameter and 1000 mm length respectively. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. All tests were performed at a filed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, 300 kg/$m^2$s. The experimental result showed that flow condensation HTCs increase as the quality, mass flux, and latent heat of condensation increase. At the same mass flux, the HTCs of R32 and R142b were higher than those of R22 by 35~45% and 7~14% respectively while HTCs of R134a and Rl23 were similar to those of R22. On the other hand, HTCs of Rl25 and Rl2 were lower than those of R22 by 28 ~30% and 15 ~25% respectively Finally, a new correlation for flow condensation HTCs was developed by modifying Dobson and Chato's correlation with the latent heat of condensation considered. The correlaton showed an average deviation of 13.1% for all pure fluids data indicating an excellent agreement.

Evaporating Heat Transfer Characteristics of R-l34a in a Horizontal Smooth Channel

  • Pamitran, A.S.;Choi, Kwang-Il;Oh, Jong-Taek;Oh, Hoo-Kyu
    • International Journal of Air-Conditioning and Refrigeration
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    • v.14 no.4
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    • pp.156-165
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    • 2006
  • Convective boiling heat transfer coefficients were measured in a horizontal minichannel with R-l34a. The test section was made of stainless steel tube with an inner diameter of 3.0 mm and a length of 2m. It was uniformly heated by applying electric current directly to the tube. Local heat transfer coefficients were obtained for heat fluxes from 10 to $40kW/m^2$, mass fluxes from 200 to $600kgT/m^2s$, qualities up to 1.0, and the inlet saturation temperature of $10^{\circ}C$. The experimental results were mapped on Wojtan et $al.'s^(7)$ and Wang et $al.'s^(8)$ flow pattern maps. The nucleate boiling was predominant at low vapor quality whereas the convective boiling was predominant at high vapor quality. Laminar flow appeared in the flow with minichannel. The experimental results were compared with six existing two-phase heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants was developed with mean and average deviations of 10.39% and -3.66%, respectively.

Instability of Evaporation Fronts in the Interstellar Medium

  • Kim, Jeong-Gyu;Kim, Woong-Tae
    • The Bulletin of The Korean Astronomical Society
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    • v.38 no.1
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    • pp.46.2-46.2
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    • 2013
  • The neutral component of the interstellar medium (ISM) is segregated into the cold neutral medium (CNM) and warm neutral medium (WNM) as a result of thermal instability. It was found that the CNM--WNM evaporation interface, across which the CNM undergoes thermal expansion, is linearly unstable to corrugational disturbances, in complete analogy with the Darrieus-Landau instability (DLI) in terrestrial flames. To explore dynamical consequences of the DLI in the ISM, we perform a linear stability analysis of the DLI including the effect of thermal conduction as well as nonlinear hydrodynamic simulations. We find that the DLI is suppressed at short length scales via heat transport. The linear growth time of the fastest growing mode is proportional to the square of the evaporation flow speed of the CNM relative to the interface and is typically >10 Myr. In the nonlinear stage, perturbations grow into cusp-like structure protruding toward the WNM, and soon reach a steady state where the evaporation rate is increased by a factor of 2 compared to the initial state. We demonstrate that the amplitude of the interface distortion and enhancement in evaporation rate are determined primarily by the density ratio between the CNM and WNM. Given quite a long growth time and highly subsonic velocities at saturation, the DLI is unlikely to play an important role in the ISM dynamics.

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Single-silicon TFT Structure for Kink-effect Suppression with Symmetric Dual-gate by Three Split floating N+ Zones (Kink-effect 개선을 위한 세 개의 분리된 N+ 구조를 지닌 대칭형 듀얼 게이트 단결정 TFT 구조에 대한 연구)

  • Lee, Dae-Yeon;Hwang, Sang-Jun;Park, Sang-Won;Sung, Man-Young
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.5
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    • pp.423-430
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    • 2005
  • In this paper, we have simulated a Symmetric Dual-gate Single-Si TFT which has three split floating $n^{+}$ zones. This structure reduces the kink-effect drastically and improves the on-current. Due to the separated floating $n^{+}$ zones, the transistor channel region is split into four zones with different lengths defined by a floating $n^{+}$ region. This structure allows an effective reduction of the kink-effect depending on the length of two sub-channels. The on-current of the proposed dual-gate structure is 0.9 mA while that of the conventional dual-gate structure is 0.5 mA at a 12 V drain voltage and a 7 V gate voltage. This results show a $80 {\%}$ enhancement in on-current by adding two floating $n^{+}$ zones. Moreover we observed the reduction of electric field In the channel region compared to conventional single-gate TFT and the reduction of the output conductance in the saturation region. In addition we also confirmed the reduction of hole concentration in the channel region so that the kink-effect reduces effectively.

Evaluations of load-deformation behavior of soil nail using hyperbolic pullout model

  • Zhang, Cheng-Cheng;Xu, Qiang;Zhu, Hong-Hu;Shi, Bin;Yin, Jian-Hua
    • Geomechanics and Engineering
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    • v.6 no.3
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    • pp.277-292
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    • 2014
  • Soil nailing, as an effective stabilizing method for slopes and excavations, has been widely used worldwide. However, the interaction mechanism of a soil nail and the surrounding soil and its influential factors are not well understood. A pullout model using a hyperbolic shear stress-shear strain relationship is proposed to describe the load-deformation behavior of a cement grouted soil nail. Numerical analysis has been conducted to solve the governing equation and the distribution of tensile force along the nail length is investigated through a parametric study. The simulation results are highly consistent with laboratory soil nail pullout test results in the literature, indicating that the proposed model is efficient and accurate. Furthermore, the effects of key parameters, including normal stress, degree of saturation of soil, and surface roughness of soil nail, on the model parameters are studied in detail.

Boiling Heat Transfer Characteristics of R-410A in $300{\mu}m$ Horizontal Smooth Microchannel ($300{\mu}m$ 수평미세관내 R-410A의 비등열전달 특성)

  • Choi, Kwang-Il;Ardiyansyah, Ardiyansyah;Pamitran, A.S.;Oh, Jong-Taek
    • Proceedings of the SAREK Conference
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    • 2008.11a
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    • pp.262-268
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    • 2008
  • The present paper dealt with flow heat transfer characteristics of R-410A vaporization in horizontal smooth microchannel. The test sections were made of stainless steel tube with inner diameters of 300 mm and length of 300 mm. The refrigerant was supplied with mass flux range of 260-600 kg/$m^2s$ and applied under operating heat flux range of 5-20 kW/$m^2$ using a direct electric current heating method. The in let saturation temperature was set at $10^{\circ}C$ and vapor quality up to 1.0. The influences of mass flux, heat flux and inner tube diameter on local heat transfer coefficients were presented. Comparison with existing heat transfer coefficient correlations was performed. An improved heat transfer coefficient correlation for refrigerant vaporization in microchannel based on superposition model was developed with a mean deviation of 14.01%.

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Boiling Heat Transfer Characteristics of $CO_2$ in Horizontal Smooth Microchannel (수평 microchannel의 $CO_2$ 비등열전달)

  • Choi, Kwang-Il;Ardiyansyah, Ardiyansyah;Oh, Jong-Taek
    • Proceedings of the SAREK Conference
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    • 2007.11a
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    • pp.241-246
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    • 2007
  • The present paper dealt with an experimental study of boiling heat transfer characteristics of $CO_2$. Heat transfer coefficients of the refrigerant flow inside horizontal smooth microchannel were obtained with inner tube diameter of 0.3mm and length of 300mm. The direct electric heating method was applied for supplying the heat uniformly to the refrigerant. The experiments were conducted with $CO_2$ purity of 99.99%, at saturation temperature of $10^{\circ}C$, mass flux ranges of $300{\sim}900\;kg/m^2s$, and heat flux ranges of $15{\sim}45\;kW/m^2$. While heat transfer coefficient increased with the increase of heat flux in the low quality region, the heat transfer coefficient decreased with the increase of quality in the high quality region. The heat transfer coefficients were compared with seven existing correlations with the Gungor-Winterton's(1986) correlation gave the best prediction. A new corelation to predict the two-phase flow heat transfer coefficient was developed based on the Chen(1966) correlation. The new correlation predicted the experimental data well with a mean deviation of 9.69% and average deviation of -3.03%.

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Phase Analysis of Immiscible V-Cu MA Powders by Neutron and X-ray Diffraction (비고용 V-Cu계 MA합금의 중성자 및 X선 회절에 의한 상분석)

  • Lee Chung-Hyo;Cho Jae-Moon;Lee Sang-Jin;Kim Ji-Soon
    • Korean Journal of Materials Research
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    • v.14 no.5
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    • pp.348-352
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    • 2004
  • The mechanical alloying (MA) effect in immiscible V-Cu system with positive heat of mixing was studied by not only the neutron and X-ray diffraction but also the analysis of DSC spectra. The total energy, ΔHt accumulated during MA for the mixture of $V_{50}$ $Cu_{50}$ / powders increased with milling time and approached the saturation value of 14 kJ/mol after 120 h of milling. It can be seen that the free energy difference between the amorphous phase and the pure V and Cu powders with an atomic ratio 5:5 is estimated to be 11 kJ/mol by Miedema et al. This is thermodynamically taken as one of the evidences for the amorphization. The structural changes of V-Cu MA powders were characterized by the X-ray diffraction and neutron diffraction. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. The neutron diffraction data definitely indicate that the amorphization proceeds gradually but incompletely even after 120 h of MA and bcc-Cu Bragg peaks appears after 60 h of MA.

Characteristics of inverted AlGaAs/InGaAs/GaAs power P-HEMTs with double channel (역 이중채널 구조를 이용한 전력용 AlGaAs/InGaAs/GaAs P-HEMT의 특성)

  • Ahn, Kwang-Ho;Jeong, Young-Han;Bae, Byung-Suk;Jeong, Yoon-Ha
    • Proceedings of the KIEE Conference
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    • 1996.11a
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    • pp.235-238
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    • 1996
  • An inverted double channel AIGaAs/lnGaAs/GaAs heterostructure grown by LP-MOCVD is demonstrated and discussed. Sheet carrier densities in excess of $4.5{\times}10^{12}cm^{-2}$ at 300K are obtained with a hall mobility of $5010cm^2/V{\cdot}s$. The proposed device with a $1.8{\times}200{\mu}m^2$ gate dimension reveals an extrinsic transconductance as high as 320 mS/mm and a saturation current density as high as 820 mA/mm at 300K. This is the highest current density ever reported for GaAs MODFET's with the same gate length. Significantly improvements on gate voltage swing (up to 3.5 V) and on reverse breakdown voltage (-10V) are demonstrated due to inverted structure.

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