• Title, Summary, Keyword: Thermal formation

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Thermal and Dynamical Evolution of a Gaseous Medium and Star Formation in Disk Galaxies

  • Kim, Chang-Goo;Kim, Woong-Tae;Ostriker, Eve C.
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.1
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    • pp.54.1-54.1
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    • 2011
  • Formation of self-gravitating gas clouds and hence stars in galaxies is a consequence of both thermal and dynamical evolution of a gaseous medium. Using hydrodynamics simulations including cooling and heating explicitly, we follow simultaneously thermal and dynamical evolution of galactic gas disks to study dynamics and structures of galactic spiral shocks with thermal instability and regulation of the star formation rates (SFRs). We first perform one-dimensional simulations in direction perpendicular to spiral arms. The multiphase gas flows across the arm soon achieve a quasi-steady state characterized by transitions from warm to cold phases at the shock and from cold to warm phases in the postshock expansion zone, producing a substantial fraction of intermediate-temperature gas. Next, we allow a vertical degree of freedom to model vertically stratified disks. The shock front experiences unsteady flapping motions, driving a significant amount of random gas motions, and self-gravity promotes formation of bound clouds inside spiral arms. Finally, we include the star formation feedback in both mechanical (due to supernova explosion) and radiative (due to FUV heating by young stars) forms in the absence of spiral arms. At saturation, gravitationally bound clouds form via thermal and gravitational instabilities, which are compensated by disruption via supernova explosions. We find that the FUV heating regulates the SFRs when gas surface density is low, confirming the prediction of the thermal and dynamical equilibrium model of Ostriker et al. (2010) for star formation regulation.

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Regulation of Star Formation Rates in Multiphase Galactic Disks: Numerical Tests of the Thermal/Dynamical Equilibrium Model

  • Kim, Chang-Goo;Kim, Woong-Tae;Ostriker, Eve C.
    • The Bulletin of The Korean Astronomical Society
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    • v.35 no.2
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    • pp.74.1-74.1
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    • 2010
  • Using two-dimensional numerical hydrodynamic simulations, we investigate the regulation of star ormation rates in turbulent, multiphase, galactic gaseous disks. Our simulation domain is xisymmetric, and local in the radial direction and global in the vertical direction. Our models nclude galactic rotation, vertical stratification, self-gravity, heating and cooling, and thermal onduction. Turbulence in our models is driven by momentum feedback from supernova events ccurring in localized dense regions formed by thermal and gravitational instabilities. Self-onsistent radiative heating, representing enhanced/reduced FUV photons from the star formation, s also taken into account. Evolution of our model disks is highly dynamic, but reaches a quasi-teady state. The disks are overall in effective hydrostatic equilibrium with the midplane thermal ressure set by the vertical gravity. The star formation rate is found to be proportional pproximately linearly to the midplane thermal pressure. These results are in good agreement with the predictions of a recent theory by Ostriker, McKee, and Leroy (2010) for the thermal/dynamic equilibrium model of star formation regulation.

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Formation of Thermal Bubble from Particle-Filled Microcavity (미세 입자로 충전된 캐비티에서의 열 기포 형성)

  • Jeong, Kwang-Hun;Lee, Heon-Ju;Chang, Young-Soo;Lee, Yoon-Pyo;Kim, Ho-Young
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.3
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    • pp.248-255
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    • 2007
  • Thermal bubble formation is a fundamental process in nucleate boiling heat transfer and many microelectromechanical thermal systems. One of the established facts is that heterogeneous nucleation is originated from vapors trapped inside cavities. Based on this, we performed an experimental study on the formation of thermal bubbles from microcavity fabricated by microfabrication technology on a copper plate. The cavity was filled with aluminum particles to enhance thermal bubble formation. We observed the thermal bubble behaviors, such as bubble incipience, diameter, frequency and coalescence during nucleate boiling. The experimental data showed that the superheat required to trigger the bubble formation was significantly reduced when the cavity was filled with microparticles. We found that the initial increase of superheat led to the increase of both the departure diameter and frequency while the further increase of superheat caused multiple bubbles to coalesce resulting in the decrease of departure frequency.

Numerical Analysis of Pressure and Temperature Effects on Residual Layer Formation in Thermal Nanoimprint Lithography

  • Lee, Ki Yeon;Kim, Kug Weon
    • Journal of the Semiconductor & Display Technology
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    • v.12 no.2
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    • pp.93-98
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    • 2013
  • Nanoimprint lithography (NIL) is a next generation technology for fabrication of micrometer and nanometer scale patterns. There have been considerable attentions on NIL due to its potential abilities that enable cost-effective and high-throughput nanofabrication to the display device and semiconductor industry. To successfully imprint a nanosized pattern with the thermal NIL, the process conditions such as temperature and pressure should be appropriately selected. This starts with a clear understanding of polymer material behavior during the thermal NIL process. In this paper, a filling process of the polymer resist into nanometer scale cavities during the thermal NIL at the temperature range, where the polymer resist shows the viscoelastic behaviors with consideration of stress relaxation effect of the polymer. In the simulation, the filling process and the residual layer formation are numerically investigated. And the effects of pressure and temperature on NIL process, specially the residual layer formation are discussed.

Formation Kinetic Study of Thermal Products of Tocopherols

  • Chung, Hae-Young
    • Preventive Nutrition and Food Science
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    • v.12 no.3
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    • pp.131-134
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    • 2007
  • The kinetic analyses for thermal products of alpha-, gamma- and delta-tocopherols during heating as functions of temperature and time were studied. Alpha-, gamma- and delta-tocopherols dissolved in glycerol were heated at $100{\sim}200^{\circ}C$ for $5{\sim}60$ min. The thermal products were separated by hexane extraction and analyzed by HPLC using a reversed phase ${\mu}-Bondapak$ $C_{18}-column$ with two kinds of elution solvents in a gradient mode. The formation kinetics of thermal products of tocopherols followed a first-order kinetic model. The formation rate of thermal products of tocopherols was dependent on heating temperatures and heating times. The activation energy and enthalpy for the thermal products of ${\gamma}-and$ ${\delta}-tocopherols$ were higher than those for ${\alpha}-tocopherol$ as in the case of the oxidative degradation kinetics of tocopherol. The magnitude order of the activation energy was ${\gamma}->{\delta}->{\alpha}-tocopherol$.

Thermal stability enhancement of silicide by kinetic modifications (Kinetics 수정에 의한 실리사이드의 열적 안정성 향상에 대한 연구)

  • Nam, Hyoung-Gin
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.8 no.5
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    • pp.1042-1046
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    • 2007
  • In this study, we investigated the mechanism responsible for the thermal stability of CoSi by addition of a foreign chemical element. Addition of W was found to increase the heat of formation of CoSi. This increase was claimed to inhibit the glass formation, which is preferred by silicide formation kinetics depicted by the maximum system energy degradation rate. In this case, there forms at the interface between CoSi and Si wafer a crystalline structure, the effective diffusion coefficient of which is much less than the self-diffusion rate provided by the glass. It was stated that the phase transition requires a higher thermal energy as the consequence, thereby enhancing the thermal stability of CoSi.

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Numerical analysis of NOx formation characteristics in CH$_{4}$-air jet diffusion flame (CH$_{4}$-공기 분류 확산화염의 NOx 생성특성에 관한 수치해석)

  • O, Chang-Bo;Lee, Chang-Eon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.2
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    • pp.193-204
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    • 1998
  • Numerical analysis was performed with multicomponent transport properties and detailed reaction mechanisms for axisymmetric 2-D CH$_{4}$ jet diffusion flame. Calculations were carried out twice with the $C_{2}$-Thermal Mechanism including $C_{2}$ and thermal NO reactions and the $C_{2}$-Full Mechanism including prompt NO reactions in addition to the above $C_{2}$-Thermal NO mechanism. The results show that the flame structures such as flame temperature, major and minor species concentration are indifferent to respective mechanisms. The production path of Thermal NO is dominant comparing with that of Prompt NO in total NO production of pure CH$_{4}$ jet diffusion flame. This is because thermal NO mechanism mainly contributes to positive formation of NO in the whole flame region, but Prompt NO mechanism contributes to negative formation in the fuel rich region. In addition, 0$_{2}$ penetration near the nozzle outlet affects the flame structures, especially N0$_{2}$ formation characteristics.

Evaluation of Thermal Conductivity for Grout/Soil Formation Using Thermal Response Test and Parameter Estimation Models (열응답 시험과 변수 평가 모델을 이용한 그라우트/토양 혼합층의 열전도도 산정)

  • Sohn Byong Hu;Shin Hyun Jun;An Hyung Jun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.2
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    • pp.173-182
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    • 2005
  • The Performance of U-tube ground heat exchanger for geothermal heat Pump systems depends on the thermal properties of the soil, as well as grout or backfill materials in the borehole. In-situ tests provide a means of estimating some of these properties. In this study, in-situ thermal response tests were completed on two vertical boreholes, 130 m deep with 62 mm diameter high density polyethylene U-tubes. The tests were conducted by adding a monitored amount of heat to water over a $17\~18$ hour period for each vertical boreholes. By monitoring the water temperatures entering and exiting the loop and heat load, overall thermal conductivity values of grout/soil formation were determined. Two parameter estimation models for evaluation of thermal response test data were compared when applied on the same temperature response data. One model is based on line-source theory and the other is a numerical one-dimensional finite difference model. The average thermal conductivity deviation between measured data and these models is of the magnitude $1\%$ to $5\%$.

Formation Temperature Dependence of Thermal Stability of Nickel Silicide with Ni-V Alloy for Nano-scale MOSFETs

  • Tuya, A.;Oh, S.Y.;Yun, J.G.;Kim, Y.J.;Lee, W.J.;Ji, H.H.;Zhang, Y.Y.;Zhong, Z.;Lee, H.D.
    • Proceedings of the IEEK Conference
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    • pp.611-614
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    • 2005
  • In this paper, investigated is the relationship between the formation temperature and the thermal stability of Ni silicide formed with Ni-V (Nickel Vanadium) alloy target. The sheet resistance after the formation of Ni silicide with the Ni-V showed stable characteristic up to RTP temperature of $700\;^{\circ}C$ while degradation of sheet resistance started at that temperature in case of pure-Ni. Moreover, the Ni silicide with Ni-V indicated more thermally stable characteristic after the post-silicidation annealing. It is further found that the thermal robustness of Ni silicide with Ni-V was highly dependent on the formation temperature. With the increased silicidation temperature (around $700\;^{\circ}C$), the more thermally stable Ni silicide was formed than that of low temperature case using the Ni-V.

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Effect of $CO_2$ Addition on Flame Structure and NOx Formation of $CH_4-Air$ Counterflow Diffusion Flames ($CO_2$ 첨가가 $CH_4$-공기 대향류 확산화염의 구조 및 NOx 생성에 미치는 영향)

  • Lee, S.R.;Han, J.W.;Lee, C.E.
    • Journal of the Korean Society of Combustion
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    • v.4 no.2
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    • pp.97-108
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    • 1999
  • This numerical study was to investigate the effect of $CO_2$ addition on the structures and NOx formation characteristics in $CH_4$ counterflow diffusion flame. The importance of radiation effect was identified and $CO_2$ addition effect was investigated in terms of thermal and chemical reaction effect. Also the causes of NOx reduction were clarified by separation method of each formation mechanisms. The results were as follows : The radiation effect was intensified by $CO_2$ addition. Thermal effect mainly contributed to the changes in flame structure and the amount of NO formation but the chemical reaction effect also cannot be neglected. The reduction of thermal NO was dominant with respect to reduction rate, but that of prompt NO was dominant with respect to total amount.

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