• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.

• Journal of IKEEE
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• v.6 no.2 s.11
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• pp.136-145
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• 2002

The simulator for the analysis of the lattice temperature under the steady-state condition is developed. The heat flow equation using the Slotboom variables is discretized and the integration method of the thermal conductivity without using the numerical analysis method is presented. The simulations are executed on the $N^+P$ junction diode and BJT to verify the proposed method. The average relative error of the lattice temperature of $N^+P$ diode compared with DAVINCI is 2% when 1.4[V] forward bias is applied and the average relative error of the lattice temperature of BJT compared with MEDICI is 3% when 5.0[V] is applied to the collector contact and 0.5[V] is applied to the base contact. BANDIS using the proposed method of integration of thermal conductivity needs 3.45 times of matrix solution to solve one bias step and DAVINCI needs 5.1 times of matrix solution MEDICI needs 4.3 times of matrix solution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1959-1970
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• 1996

Effects of oscillatory flow upon heat transfer characteristics have been studied experimentally for oscillating flow in a circular tube. The experimental apparatus was designed to simulate the heat exchangers of the Stirling or Vuilleumier cycle machines and the test section consists of heater and cooler. Measurements were presented of heat flux, axial wall temperature distribution, and radial temperature profile of the working fluid for several cases of oscillation frequency and swept distance ratio. The influences of two main parameters, frequency and tidal displacement of the oscillation were investigated. Then the heat transfer coefficient at the heater is obtained. The carried by the authors with a assumption of oscillatory laminar slug flow.

• Korean journal of applied entomology
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• v.56 no.1
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• pp.1-18
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• 2017

Temperature-dependent development model is an essential component for forecasting models of insect pests as well as for insect population models. This study reviewed the nonlinear models which explain the relationship between temperature and development rate of insects. In the present study, the types of models were classified largely into empirical and biophysical model, and the groups were subdivided into subgroups according to the similarity of mathematical equations or the connection with original idea. Empirical models that apply analytical functions describing the suitable shape of development curve were subdivided into multiple subgroups as Stinner-based types, Logan-based types, performance models and Beta distribution types. Biophysical models based on enzyme kinetic reaction were grouped as monophyletic group leading to Eyring-model, SM-model, SS-mode, and SSI-model. Finally, we described the historical development and characteristics of non-linear development models and discussed the availability of models.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.717-726
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• 2006

Traditional external post-tensioning method using either steel bars or tendons is commonly used as a retrofitting method for steel composite bridges. However, the method has some disadvantages such as stress concentration at anchorages and inefficient load-carrying capability of live loads. Multi-stepwise prestressing method using thermal expanded coverplate is a newly proposed prestressing method, which was originally developed for prestressing steel structures. A new retrofitting method for steel girder bridges founded on a simple concept of thermal expansion and contraction of cover plate, the method is a hybrid of and combines the advantages of external post-tensioning and thermal prestressing. In this paper, basic concepts of the method are presented and an illustrative experiment is introduced. From actual experimental data, the thermal prestressing effect was substantiated and the FEM approach for its analysis was verified. The retrofitting effects ofa single-span bridge were analyzed and the feasibility of the developed method was examined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.33-39
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• 2007

This paper is aimed at the development of a software that predicts the surface temperature profiles of three-dimensional objects on the ground by considering the spectral solar radiation through the atmosphere. The spectral solar radiation through the atmosphere is modeled by using the well-known LOWTRAN7 code which analyzes the detailed spectral transmission characteristics by considering the atmospheric gas layers. In this paper, the transient temperature distribution over a cylinder is calculated by using the semi-implicit method. The spectral radiative surface properties such as the absorptivity and emissivity of the objects are used to model the effects of the solar irradiation and the surface emission. Both the detailed spectral modeling and the simple total modeling for the solar radiation absorption show fairly good agreement with each other by showing less than 3% difference in surface temperature.

• Polymer(Korea)
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• v.28 no.5
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• pp.361-366
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• 2004

The poling characteristics of PVDF (poly(vinylidene fluoride)) film was investigated by measuring the electric voltage generated by the external load for the distributed tactile sensor applications. The poling conditions for the PVDF films were controlled by changing temperature and electric field, and the resulting crystal structure of the $\beta$-phase crystal was confirmed by FT-IR, DSC, and XRD experiments. The $\beta$-phase crystal was increased with the poling temperature and poling voltage, and subsequently the permittivity of the Poled PVDF films was increased. Finally, the prototype tactile sensor was tested by a 8 $\times$ 8 may circuit exhibiting high voltage signal for the highly poled PVDF films.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.647-653
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• 2007

In ready mixed concrete factory, in case of using the high molecular additive in winter especially the liquid additive for the early strength, it is required to check the stability. In this research, the freezing and gelling characteristics of the liquid additive for the early strength is reviewed, the material and mechanical solution are proposed to that the practical quality control method will be suggested. As the result, the Freezing temperature of the liquid additive for the early strength is $-11.8^{\circ}C$, and it is the lower than the temperature at which the strength is shown. By making with sodium silicate of $37{\pm}0.5%$ designed by $SiO_2\;and\;Na_2O$ in 0.31 of mol ratio, it minimizes the gelling at the lower temperature. On the other hand, facilities for storing and supplying the material should be set at $40^{\circ}C$ so the temperature distribution is well spreaded for practical operation.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.39-49
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• 2007

The objective of this study was to investigate features of transverse crack occurrence and propagation in continuously reinforced concrete pavement(CRCP) when subjected to environmental loading. The finite element model of CRCP was developed and the element removal method was implemented to predict the crack propagation process. To investigate the effect of the type of environmental loading on the CRCP behavior and cracking aspects, the following three different cases were considered: (1) the temperature gradient between top and bottom of the slab does not vary and the constant temperature drop throughout the depth occurs; (2) the temperature at the slab bottom does not vary and the temperature gradient increases; and (3) the temperature between the mid-depth and the bottom of the slab is the same and does not vary and the temperature at the top decreases. The analysis results showed that the crack occurrence and propagation through the depth of the slab in CRCP were significantly affected by the type of environmental loading. The changes in stress distribution and displacements during the crack occurrence and propagation process could also be investigated.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.938-943
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• 2000

TiCl$_4$, 물 및 1-propanol의 혼합용액으로부터 미립 TiO$_2$분말 제조시, 1-propanol과 물의 부피비, 반응온도, 반응유지시간 및 TiCl$_4$mole 농도에 따른 분말 특성 및 결정상 생성에 대해 조사하였다. 반응온도가 3$0^{\circ}C$ 이상일 때 Ti 수화물의 초기 침전이 생성되었고 반응온도가 TiCl$_4$mole 농도가 증가함에 따라 입자크기는 증가하였고 $600^{\circ}C$ 하소시 1-propanol과 물의 부피비가 2보다 크고 반응온도가 7$0^{\circ}C$보다 낮을 때 주결정상은 anatase였다. 입자크기가 미세하고 입자크기 분포가 좁은 범위를 갖는 조건은 1-propanol과 물의 부피비가 2, 반응온도가 7$0^{\circ}C$, TiCl$_4$mole 농도가 0.2 mole/ι일 때였으며, 결정상의 생성은 1-propanol과 물의 부피비가 2, 반응온도가 3$0^{\circ}C$ 이상일 때 anatase에서 rutile로 전이하는 온도가 높아졌다. 이와 같은 반응인자에 따른 효과는 용매의 유전상수, 티타니아의 용해도, 입자의 표면전위 등의 효과와 관계가 있었다.