• 국제초고층학회논문집
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• 제4권4호
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• pp.283-290
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• 2015

Crack control remains a primary concern for mass concrete structures, where the majority of cracking is caused by temperature changes during the hydration process. One-time pouring is a useful construction method for mass concrete structures. The suitability of this method for constructingon of the Shanghai Tower's mass concrete foundation slab of Shanghai Tower is considered here by a numerical simulation method based on a 6- meter- thick slab. Some of the conclusions, which can be verified by monitoring results conducted during construction, are as follows. The temperature gradient is greater in the vertical direction than in the radial direction, therefore, the vertical temperature gradient should be carefully considered for the purpose of crack control. Moreover, owing to cooling conditions at the surfaces and the cement mortar content of the slab, the temperatures and temperature gradients with respect to time vary according to the position within the slab.

• 비파괴검사학회지
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• 제22권6호
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• pp.609-620
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• 2002

It is well known that during tensile testing, a part of the mechanical work done on the specimen is transformed into heat energy. However, the ultimate temperature rise and the rate of temperature rise is related to the nature of the material, conditions of the test and also to the deformation behaviour of the material during loading. The recent advances in infrared sensors and image/data processing techniques enable observation and quantitative analysis of the heat energy dissipated during such tensile tests. In this study, infrared imaging technique has been used to characterise the tensile deformation in AISI type 316 nuclear grade stainless steel. Apart from identifying the different stages during tensile deformation, the technique provided an accurate full-field temperature image by which the point and time of strain localization could be identified. The technique makes it possible to visualise the region of deformation and failure and also predict the exact region of fracture in advance. The effect of thermal gradients on plastic flow in the case of interrupted straining revealed that the interruption of strain and restraining at a lower strain rate not only delays the growth of the temperature gradient, but the temperature rise per unit strain decreases. The technique is a potential NDE tool that can be used for on-line detection of thermal gradients developed during extrusion and metal forming process which can be used for ensuring uniform distribution of plastic strain.

• Advances in aircraft and spacecraft science
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• 제10권1호
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• pp.19-49
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• 2023

The present study proposes a theoretical and numerical investigation on the dynamic response behaviour of a functional graded (FG) ceramic-metal tapered rotor shaft system, by the differential quadrature finite elements method (DQFEM) to identify the natural frequencies for modelling and analysis of the structure with suitable validations. The purpose of this paper is to explore the influence of heat gradients on the natural frequency of rotation of FG shafts via three-dimensional solid elements, as well as a theoretical examination using the Timoshenko beam mode, which took into account the gyroscopic effect and rotational inertia. The functionally graded material's distribution is described by two distribution laws: the power law and the exponential law. To simulate varied thermal conditions, radial temperature distributions are obtained using the nonlinear temperature distribution (NLTD) and exponential temperature distribution (ETD) approaches. This work deals with the results of the effect on the fundamental frequencies of different material's laws gradation and temperature gradients distributions. Attempts are conducted to identify adequate explanations for the behaviours based on material characteristics. The effect of taper angle and material distribution on the dynamic behaviour of the FG conical rotor system is discussed.

• 한국환경생태학회지
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• 제31권3호
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• pp.279-286
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• 2017

$CO_2$농도와 온도의 상승으로 인한 지구온난화가 진행되었을 때 광, 수분 그리고 유기물 구배에 따른 멸종위기식물인 황근의 생육과 생태적 지위폭의 변화를 알아보았다. 대조구(야외)와 처리구($CO_2$ + 온도 상승구)로 나누어 각각 광, 수분 그리고 유기물구배를 두어 재배하였다. 그 연구결과, 황근은 낮은 광량보다 높은 광량을 선호하나, 광량이 $787{\pm}77.76{\mu}mol\;m^{-2}s^{-1}$을 넘어가면 높은 광량이라 하더라도 생육이 어려웠다. 또한 유기물이 없거나(0%) 너무 많은 토양(20%)에서는 생육이 어려웠다. 그러나 수분 구배에 따른 경향이 보이지 않았다. 황근의 고사율은 대조구보다 처리구에서 광량이 높은 조건을 제외한 모든 구배에서 높았다. 이는 $CO_2$와 온도가 상승하면 광에 대한 내성범위가 좁아진다는 것을 의미한다. 대조구와 처리구를 비교하였을 때, 수분구배에 따른 경향은 보이지 않았다. 유기물구배에서는 대조구보다 처리구에서 모두 고사율이 낮았는데, 이는 유기물에 대한 내성의 범위가 넓어진 것을 의미한다. 황근의 생태적 지위폭은 처리구가 대조구보다 광 구배에서 30.1% 좁아졌으며, 수분 구배에서 8.6% 그리고 유기물 구배에서 30% 넓어졌다. 따라서 $CO_2$농도와 온도의 증가로 인한 지구온난화가 진행되면, 황근의 생육은 광량에 의해서 제한될 것으로 판단된다.

• Journal of Ecology and Environment
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• 제42권4호
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• pp.278-284
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• 2018

Plant functional traits have been shown to be useful to understand how and why ecosystems and their components vary across environmental heterogeneity or gradients. This study investigated how plant functional (leaf) traits vary according to an elevation-associated environmental gradient. Environmental gradients (mean annual temperature and precipitation) were quantified, and leaf traits (leaf area, specific leaf area, leaf nitrogen, leaf phosphorus, leaf carbon, and leaf C/N ratio) of the understory woody plant species Acer pseudosieboldianum were examined across an elevational gradient ranging from 600 to 1200 m in a Baegunsan Mountain in Gwangyang-si, Jeollanam-do, South Korea. The results showed that mean annual temperature and precipitation decreased and increased along with elevation, respectively. Leaf area of the plant species decreased slightly with increasing elevation, while specific leaf area did not differ significantly. Leaf nutrients (nitrogen, phosphorus, and carbon concentrations) were higher at high elevations, but leaf C/N ratio decreased with elevation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1188-1195
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• 2007

The vertical forces in rail fasteners at areas of bridge transitions near the embankment and on the pier will occur due to different deformations of adjoining bridges caused by the trainloads, the settlement of supports, and the temperature gradients. The up-lifting forces is not large problem in the blast track because the elasticity of blast and rail pad buffs up-lifting effect. But, it is likely to be difficult to ensure the serviceability of the railway and the safety of the fastener in the end in that concrete slab track consist of rail, fastener, and track in a single body, delivering directly the up-lifting force to the fastener if the deck is bended because of various load cases, such as the end rotation of the overhang due to the vertical load, the bending of pier due to acceleration/braking force and temperature deviation, the settlement of embankment and pier, the temperature deviation of up-down deck and front-back pier, and the rail deformation due to wheel loads. The analysis of the rail fastener is made to verify the superposed tension forces in the rail fastener due to various load cases, temperature gradients and settlement of supports. The potential critical fasteners with the highest uplift forces are the fastener adjacent to the civil joint. The main influence factors are the geometry of the bridge such as, the beneath length of overhang, relative position of bridge bearing and fastener, deflection of bridge and the vertical spring stiffness of the fastener.

• Journal of the Korean Wood Science and Technology
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• 제26권3호
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• pp.1-8
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• 1998

Western redcedar timber, 26 by 26cm in cross section and by 200cm long, was dried in a laboratory radio-frequency/vacuum kiln under 65torr of ambient pressure and a fixed frequency of 6.78MHz for the potential rapidly dry large timber. All process data were collected and saved in a computer through a data acquisition system. The temperature in the middle of timber was higher than temperature at the quarter point of timber length and thickness. Temperature gradients developed in the longitudinal and transverse direction of timber. The pressure in the middle of timber was higher than pressure at the quarter point of timber length. The pressure in the middle of timber was lower in the early stage of drying, and higher in the latter stage of drying than pressure at the quarter point of timber thickness. Power density was very highest during heating period and then gradually decreased. The drying curve was approximately linear and the total drying time was 27 hours from an initial moisture content(MC) of 48.6 percent to a final Me of 19.2 percent with only a few mild internal checks in the middle location of timber.

• Journal of Acupuncture Research
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• 제26권1호
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• pp.111-119
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• 2009

Objectives : The purpose of this study is to investigate the mechanism and effect of moxa bucket moxibustion, to be used as the quantitative data through the measurement of temperature, and to grasp the thermodynamic characteristics of moxa bucket moxibustion. Methods : We have selected the moxa bucket moxibustion. We have made a comparative study of the thermodynamic characteristics of moxa bucket moxibustion. We have examined combustion times, temperatures, temperature gradients in each period during a combustion of moxa bucket moxibustion made by oak wood. Results : 1. We could design the moxa bucket moxibustion so that it has $57.6^{\circ}C$ maximum temperature with 7g weight and 10mm height, if we use more weight of moxa or lower height of moxa, we can observe relatively elevated maximum temperature. We observed the maximum temperature following the measuring position of moxa bucket and we could see higher temperature at the center of the moxa bucket and lower temperature at the side of the moxa bucket. 2. We could design the moxa bucket moxibustion with 5g moxa and 10mm height so that it has 0.12 $1^{\circ}C/sec$ of maximum temperature gradient, and it has relatively high temperature gradient at lower weight and height condition. 3. We could design the moxa bucket moxibustion with 7g moxa and 15mm height so that it has 4,135sec of the longest effective temperature combustion time. If we use more weight of moxa or higher height of moxa, we can observe relatively extended effective temperature combustion time. Conclusions : We observed the longest effective combustion time following the measuring position of moxa bucket. We can see a higher temperature at the center of the moxa bucket and a lower temperature at the side of the moxa bucket.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1624-1638
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• 1996

A study of thermophoretic particle deposition has been carried out for a particle laden stagnation flow considering the effect of radiative heat transfer. Energy, concentration and radiative transfer equations are all coupled and have been solved iteratively assuming that absorption and scattering coefficients were proportional to the local concentration of particles. Radiative heat transfer was shown to strongly affect the profiles of temperature and particle concentration. e. g., radiation increases the thickness of thermal boundary layer and wall temperature gradients significantly. As the wall temperature gradients increase, the particle concentration at the wall decreases due to thermophoretic particle transport. The deposition rate that is thermophoretic velocity times particle concentration at the wall decreases as the effects of radiation increases. The effects of optical thickness, conduction to radiation parameter and wall emissivity have been determined. The effects of anisotropic scattering are shown as insignificant.

• 한국정밀공학회지
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• 제20권10호
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• pp.183-190
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• 2003

Major device failures such as die cracking, interfacial delamination and warpage in flip chip packages are due to excessive heat and thermal gradients- There have been significant researches toward understanding the thermal performance of electronic packages, but the majority of these studies do not take into account the combined effects of thermo-mechanical interactions of the different package constituents. This paper investigates the thermo-mechanical performance of flip chip package constituents based on the finite element method with thermo-mechanically coupled elements. Delaminations with different lengths between the silicon die and underfill resin interfaces were introduced to simulate the defects induced during the assembly processes. The temperature gradient fields and the corresponding stress distributions were analyzed and the results were compared with isothermal case. Parametric studies have been conducted with varying thermal conductivities of the package components, substrate board configurations. Compared with the uniform temperature distribution model, the model considering the temperature gradients provided more accurate stress profiles in the solder interconnections and underfill fillet. The packages with prescribed delaminations resulted in significant changes in stress in the solder. From the parametric study, the coefficients of thermal expansion and the package configurations played significant roles in determining the stress level over the entire package, although they showed little influence on stresses profile within the individual components. These observations have been implemented to the multi-board layer chip scale packages (CSP), and its results are discussed.