• 한국세라믹학회지
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• 제29권3호
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• pp.189-194
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• 1992

In order to grow a 127.86$^{\circ}$rotated LiNbO3 single crystal with good characteristics of surface acoustic wave (SAW) up to 80 mm in diameter, the temperature gradient of furnace, the growth rate and the rotation rate of crystal were changed. We could grow a crystal which had few macro defects at the conditions of temperature gradient as 30~6$0^{\circ}C$/cm, growth rate as 5 mm/hr and rotation rate as 8 rpm. The experimental ranges of the growth conditions are as follows. Temperature gradient was varied from 20 to 20$0^{\circ}C$/cm, growth rate as 5~7 mm/hr and crystal rotation rate as 6~12rpm.

• Advances in nano research
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• 제12권3호
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• pp.231-251
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• 2022

Dynamic behavior of temperature-dependent Reddy functionally graded (RFG) nanobeam subjected to thermomagnetic effects under the action of moving point load is carried out in the present work. Both symmetric and sigmoid functionally graded material distributions throughout the beam thickness are considered. To consider the significance of strain-stress gradient field, a material length scale parameter (LSP) is introduced while the significance of nonlocal elastic stress field is considered by introducing a nonlocal parameter (NP). In the framework of the nonlocal strain gradient theory (NSGT), the dynamic equations of motion are derived through Hamilton's principle. Navier approach is employed to solve the resulting equations of motion of the functionally graded (FG) nanoscale beam. The developed model is verified and compared with the available previous results and good agreement is observed. Effects of through-thickness variation of FG material distribution, beam aspect ratio, temperature variation, and magnetic field as well as the size-dependent parameters on the dynamic behavior are investigated. Introduction of the magnetic effect creates a hardening effect; therefore, higher values of natural frequencies are obtained while smaller values of the transverse deflections are produced. The obtained results can be useful as reference solutions for future dynamic and control analysis of FG nanobeams reinforced nanocomposites under thermomagnetic effects.

• 대한금속재료학회지
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• 제46권3호
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• pp.150-158
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• 2008

The temperature distribution of high speed tool steel rod has been studied during high speed hot rolling procedures. The tool steel rod shows severe temperature gradient during rolling procedures and the temperature at the center of rod are much higher than that at the surface of rod. This temperature gradient accumulated after every rolling procedure and the center of rolled rod could be remelt in some procedures to cause inside defects. In this study, the temperature distribution was simulated using finite element method and the processing parameters such as rolling speed, cooling condition, have been discussed to prevent the temperature increases at the center of rod.

• Structural Engineering and Mechanics
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• 제51권4호
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• pp.627-641
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• 2014

Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (${\alpha}$), austenite (${\gamma}$), bainite (${\beta}$) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range $1000-1200^{\circ}C$ and strain rate 0.01-1 s-1 and a sound agreement is found.

• 한국자동차공학회논문집
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• 제4권1호
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• pp.208-217
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• 1996

Instantaneous surface temperature and unsteady heat flux of intake and exhaust valve in methanol fueled engine were investigate as a function of compression ratio and engine speed. To accomplish this purpose, the instantaneous temperature sensor was designed and it was installed into three point of intake and exhaust valve head to measure unsteady temperature. The unsteady heat flux at valves was evaluated using one dimensional heat conduction equation with the valve head temperature and temperature gradient. And also mean heat flux of intake and exhaust valve for each stroke were evaluated as a function of engine speed.

• 한국전기전자재료학회논문지
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• 제19권5호
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• pp.486-491
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• 2006

A research was undertaken on the thermal properties and behavior of the conductors in a controlled chamber, which was designed to implement the outdoor air temperature, heat and wind conditions. With ACSR $410mm^2$ overhead conductors, we measured the maximum temperature of the conductors and the temperature gradient from the core to the surface regions as a function of current, tension, wind velocity and outdoor air temperature. This test also provided a comparative analysis between the measured temperature values of conductors in the controlled chamber and the theoretical calculations of ANSI/IEEE at normal condition.

• Coupled systems mechanics
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• 제7권4호
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• pp.373-393
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• 2018

This paper is concerned with the wave propagation behavior of rotating functionally graded temperature-dependent nanoscale beams subjected to thermal loading based on nonlocal strain gradient stress field. Uniform, linear and nonlinear temperature distributions across the thickness are investigated. Thermo-elastic properties of FG beam change gradually according to the Mori-Tanaka distribution model in the spatial coordinate. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The governing equations are derived by Hamilton's principle as a function of axial force due to centrifugal stiffening and displacement. By applying an analytical solution and solving an eigenvalue problem, the dispersion relations of rotating FG nanobeam are obtained. Numerical results illustrate that various parameters including temperature change, angular velocity, nonlocality parameter, wave number and gradient index have significant effect on the wave dispersion characteristics of the understudy nanobeam. The outcome of this study can provide beneficial information for the next generation researches and exact design of nano-machines including nanoscale molecular bearings and nanogears, etc.

• 대한기계학회논문집
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• 제16권2호
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• pp.369-381
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• 1992

Characteristics of flow and heat transfer have been studied numerically in a square duct with a periodic pressure gradient. The flow in a duct was assumed to be fully developed and constant heat flux was imposed at the surfaces of a square duct. The distributions of axial velocity and time-space averaged temperature are investigated with angular velocity and amplitude ratio at a given Reynolds number 1000. When the periodic pressure gradient was imposed axially in a duct, the reverse flow may be occurred near the duct wall. The magnitude of this reverse flow increases as the amplitude ratio increases or as the angular frequency decreases. In the ranges of the amplitude ratio and the angular velocity in present investigation, the ratio of the periodic time space averaged temperature to the nonperiodic space averaged temperature has been found to be greater than one. This means that the cooling effect at the duct walls deteriorates with a periodic situation compared with nonperiodic one.

• 천문학회지
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• 제39권4호
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• pp.81-87
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• 2006

A relation between temperature and time has been constructed in the self-consistent model(SCM). This relation is used to calculate the a CMBR temperature. This temperature has been found to be 2.9K. The temperature gradient of microwave background radiation(CMBR) is calculated in the Self Consistent Model. Two relations between Hubble parameter and time derivative of the temperature, have been presented in two different cases. In the first case the temperature is treated as a function of time only, while in the other one, it is assumed to be a function in time and solid angle, beside the assumption that the universe expands adiabatically.

• Steel and Composite Structures
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• 제25권3호
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• pp.315-326
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• 2017

In this work, thermoelastic dynamic behavior of functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylinders subjected to mechanical pressure loads, uniform temperature environment or thermal gradient loads is investigated by a mesh-free method. The material properties and thermal stress wave propagation of the nanocomposite cylinders are derived after solving of the transient thermal equation and obtaining of the time history of temperature field of the cylinders. The nanocomposite cylinders are made of a polymer matrix and wavy single-walled carbon nanotubes (SWCNTs). The volume fraction of carbon nanotubes (CNTs) are assumed variable along the radial direction of the axisymmetric cylinder. Also, material properties of the polymer and CNT are assumed temperature-dependent and mechanical properties of the nanocomposite are estimated by a micro mechanical model in volume fraction form. In the mesh-free analysis, moving least squares shape functions are used to approximate temperature and displacement fields in the weak form of motion equation and transient thermal equation, respectively. Also, transformation method is used to impose their essential boundary conditions. Effects of waviness, volume fraction and distribution pattern of CNT, temperature of environment and direction of thermal gradient loads are investigated on the thermoelastic dynamic behavior of FG-CNTRC cylinders.