• Title/Summary/Keyword: Surface conduction

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A Semi-analytical Model for Depletion-mode N-type Nanowire Field-effect Transistor (NWFET) with Top-gate Structure

  • Yu, Yun-Seop
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.10 no.2
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    • pp.152-159
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    • 2010
  • We propose a semi-analytical current conduction model for depletion-mode n-type nanowire field-effect transistors (NWFETs) with top-gate structure. The NWFET model is based on an equivalent circuit consisting of two back-to-back Schottky diodes for the metal-semiconductor (MS) contacts and the intrinsic top-gate NWFET. The intrinsic top-gate NWFET model is derived from the current conduction mechanisms due to bulk charges through the center neutral region as well as of accumulation charges through the surface accumulation region, based on the electrostatic method, and thus it includes all current conduction mechanisms of the NWFET operating at various top-gate bias conditions. Our previously developed Schottky diode model is used for the MS contacts. The newly developed model is integrated into ADS, in which the intrinsic part of the NWFET is developed by utilizing the Symbolically Defined Device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce considerably well the reported experimental results.

A Study on the Electrical and Mechanical Properties of Conduction Cooling HTS SMES

  • Choi, Jae-Hyeong;Choi, Jin-Wook;Shin, H.S.;Kim, H.J.;Seong, K.C.;Kim, S.H.
    • Progress in Superconductivity and Cryogenics
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    • v.11 no.2
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    • pp.29-32
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    • 2009
  • The conduction cooling HTS SMES magnet is operated in cryogenic temperature. The insulation design at cryogenic temperature is an important element that should be established to accomplish miniaturization that is a big advantage of HTS SMES. However, the behaviors of insulators for cryogenic conditions in air or vacuum are virtually unknown. Therefore, we need active research and development of insulation concerning application of the conduction cooling HTS SMES. Specially, this paper was studied about high vacuum and cryogenic temperature breakdown and flashover discharge characteristics between cryocooler and magnet-coil. The breakdown and surface flashover discharge characteristics were experimented at cryogenic temperature and vacuum. Also, we were experimented about mechanical properties of 4-point bending test. From the results, we confirmed that about research between cryocooler and magnet-coil established basic data in the insulation design.

Measurement of Critical Heat Flux Using the Transient Inverse Heat Conduction Method in Spray cooling (비정상 열전도 역산법에 의한 분무냉각 임계열유속(CHF)의 측정에 관한 연구)

  • Kim, Yeung Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.10
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    • pp.653-658
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    • 2016
  • A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

A Comparative Study on Heat Transfer Characteristics in Tissue Model with Application of Heating or Cooling Therapeutic Modalities (조직모델에서 냉.온치료기의 열전달 특성 비교 연구)

  • Kim, Yu Jong;Shin, Kyung Min;Kim, Eun Jung;Kim, Kyung Ho;Kim, Kap Sung;Lee, Seung Deok
    • Journal of Acupuncture Research
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    • v.30 no.4
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    • pp.125-138
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    • 2013
  • Objectives : This study aimed to investigate temperature characteristics by heat transfer type of therapeutic modalities. Methods : We selected heating and cooling modalities that are frequently used in clinical by heat transfer type: conduction, convection, radiation, and conversion. We used ham as tissue model, and applied the modalities for 30 minutes. We measured real-time changed temperature($^{\circ}C$) of the surface, 2, 4, 6, 8, 10, 12, and 14 mm depth. Results : 1. In conduction-using hot pack, ice pack, and CryoStamp heating-cooling combination therapy unit($40^{\circ}C/{\sim}15^{\circ}C$), the surface temperature sharply rose close to equilibrium in first 5 minutes. 2. In convection-using smokeless moxa, temperature slowly rose to the maximum at 25-minute elapsed time. But in another convection-using CRAiS cryotherapy device, result was similar to that of conduction. 3. In radiation-using infrared lamp, result was similar to that of conduction, but not reached equilibrium during applying time. 4. In conversion-using ultrasound device, temperature was the highest at 6 mm depth, and not reached equilibrium during applying time. Conclusions : We could comprehend temperature characteristics and proper use of modalities by heat transfer type. It would be necessary to consider in vivo physical conditions in further studies.

Analysis of Hyperbolic Heat Conduction in a Thin Film (박막에서 쌍곡선형 열전도 방정식에 의한 열전도 해석)

  • 정우남;이용호;조창주
    • Journal of Energy Engineering
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    • v.8 no.4
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    • pp.540-545
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    • 1999
  • The classical Fourier heat conduction equation is invalid at temperatures near absolute zero or at very early times in highly transient heat transfer processes. In such situations, a hyperbolic equation model for heat conduction based on the modified Fourier law is introduced because the wave nature of heat propagation becomes dominant. The Fourier model and the hyperbolic model for heat conduction are analyzed by using the Green's function technique together with the integral transform. Analytical expressions for the heat flux and temperature distributions in a finite slab subjected to a periodic surface heating at one of its surfaces are presented and the results obtained from each model are compared with each other. The thermal wave implied b the hyperbolic model is shown to travel through a medium and to reflect back toward the origin at the other insulated surface. On the other hand, the heat by the Fourier model propagates at an infinite speed instantaneously after a thermal disturbance is felt throughout the medium.

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INVERSE HEAT CONDUCTION PROBLEM IN A THIN CIRCULAR PLATE AND ITS THERMAL DEFLECTION

  • Tikhe, A.K.;Deshmukh, K.C.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.9 no.2
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    • pp.75-82
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    • 2005
  • An inverse problem of transient heat conduction in a thin finite circular plate with the given temperature distribution on the interior surface of a thin circular plate being a function of both time and position has been solved with the help of integral transform technique and also determine the thermal deflection on the outer curved surface of a thin circular plate defined as $0\;{\leq}\;r\;{\leq}\;a,\;0\;{\leq}\;z\;{\leq}\;h$. The results, obtained in the series form in terms of Bessel's functions, are illustrated numerically.

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Ductile Simulation Analysis at Heat Exchanger (열교환기에서의 연성 시뮬레이션 해석)

  • Cho, Jae-Ung;Han, Moon-Sik
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.7 no.3
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    • pp.50-54
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    • 2008
  • This study is analyzed by the simulation of heat exchanger. As heat conduction happens as contact begins, the temperature increases until $70^{\circ}C$ at the contact part. The displacement increases until 33mm at its maximum and maximum equivalent stress at final stage increases 20 times as much as that of first contact. The expenses about maintenance, repair and management of parts can be reduced largely by applying the simulation about various parts of heat exchanger.

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Carrier ConDuction of Thin Film Transistors (박막 트랜지스터의 반송자 전도)

  • 마대영;김기원
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.21 no.6
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    • pp.51-55
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    • 1984
  • Band headings, at grain boundary and surface of polycrystalline thin semiconductor films, were assumed. thin film ransistor conduction theory which considered trapping at surface of semiconductor was proposed. CdSe Thin Film Transistors were fabricated. CdSe was thermal evaporated and SiO2 used as insulator was rf sputtered. Output characteristics which was calculated by conduction theory were compared with experimental results.

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Analysis of Keyhole Formation and Stability in Laser Spot Welding (레이저 점 용접의 키홀 발생과 안정성에 대한 해석)

  • 고성훈;이재영;유중돈
    • Journal of Welding and Joining
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    • v.20 no.4
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    • pp.484-490
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    • 2002
  • The formation and stability of stationary laser weld keyholes were investigated using a numerical simulation. The effect of multiple reflections in the keyhole was estimated using the ray tracing method, and the free surface profile, flow velocity and temperature distribution were calculated numerically. In the simulation, the keyhole was formed by the displacement of the melt induced by evaporation recoil pressure, while surface tension and hydrostatic pressure opposed cavity formation. A transition mode having the geometry of the conduction mode with keyhole formation occurred between the conduction and keyhole modes. At laser powers of 500W and greater, the protrusion occurred on the keyhole wall, which resulted in keyhole collapse and void formation at the bottom. Initiation of the protrusion was caused mainly by collision of upward and downward flows due to the pressure components, and Marangoni flow had minor effects on the flow patterns and keyhole stability.bility.

Contour Integral Method for Crack Detection

  • Kim, Woo-Jae;Kim, No-Nyu;Yang, Seung-Yong
    • Journal of the Korean Society for Nondestructive Testing
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    • v.31 no.6
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    • pp.665-670
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    • 2011
  • In this paper, a new approach to detect surface cracks from a noisy thermal image in the infrared thermography is presented using an holomorphic characteristic of temperature field in a thin plate under steady-state thermal condition. The holomorphic function for 2-D heat flow field in the plate was derived from Cauchy Riemann conditions to define a contour integral that varies according to the existence and strength of a singularity in the domain of integration. The contour integral at each point of thermal image eliminated the temperature variation due to heat conduction and suppressed the noise, so that its image emphasized and highlighted the singularity such as crack. This feature of holomorphic function was also investigated numerically using a simple thermal field in the thin plate satisfying the Laplace equation. The simulation results showed that the integral image selected and detected the crack embedded artificially in the plate very well in a noisy environment.