• Geomechanics and Engineering
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• 제16권4호
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• pp.415-421
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• 2018

A location determining method is proposed for critical sliding surface in the stability analysis of the filling materials in karst caves. First, a preliminary location of the sliding surface is determined based on simulation results which includes displacement contour and plastic zone. The sliding surface will locate on the bottom contact interface when the friction angle is relative small. However, a weakened contact interface always becomes the critical sliding surface no matter what the friction angle is. Then when the friction angle becomes larger, the critical sliding surface inside fillings can be determined by a parabola, the coefficient of which increases linearly with the friction angle under the same cohesion. Finally, the critical sliding surface approximately remains unchanged with friction angle. The influence of cohesion is similar to that of friction angle. Although affected by shape, size or position of the karst cave, the critical sliding surface mainly depends on both friction angle and cohesion. Thus, this method is always useful in determining the critical sliding surface.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1095-1099
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• 2008

Critical state theory involves two state boundary surface. One is Roscoe surface and the other is Hvorslev surface. The shape of these boundary surface was changed because of several parameters : Critical state constant(M), spacing ratio (r) and critical state pore pressure coefficient($\wedge$). As these constants make difference to each model and the way of solution, they may affect the shape of state boundary surface. Specially, spacing ratio (r) is important. On this study, triaxial compression test was performed using remolded weathered mudstone soil and investigated variation of state boundary surface because of spacing ratio. In the results of prediction, critical state point was located highly and the shape of boundary surface was changed more tightly curve as decreasing spacing ratio.

• Advances in nano research
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• 제12권4호
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• pp.365-374
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• 2022

Intermediate filaments are the mechanical ropes for both cytoskeleton and nucleoskeleton of the cell which provide tensile force to these skeletons. In providing the mechanical support to the cell, they are likely to buckle. We used conventional Euler buckling model to find the critical buckling force under different boundary conditions which they assume during different functions. However, there are many experimental and theoretical studies about other cytoskeleton components which demonstrate that due to mechanical coupling with the surrounding surface, the critical buckling force increases considerably. Motivated with these results, we also investigated the influence of surface effects on the critical buckling force of intermediate filaments. The surface effects become profound because of increasing ratio of surface area of intermediate filaments to bulk at nano-scale. The model has been solved analytically to obtain relations for the critical forces for the buckling of intermediate filaments without and with surface effects. We found that critical buckling force with surface effects increases to a large extent due to mechanical coupling of intermediate filaments with the surrounding surface. Our study may be useful to develop a unified experimental protocol to characterize the physical properties of Intermediate filaments and may be helpful in understanding many biological phenomenon involving intermediate filaments.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.980-983
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• 2002

In micro-machining, diamond tool is commonly used because it brings much better micro-machinability due to its edge sharpness. However, it is a big question even how thinly the sharp edge of a diamond tool can cut a ship from the workpiece surface. This paper is to investigate the critical cutting depth, at which the dominant cutting mode changes from chip formation to burnishing or vice versa, for a given edge radius. The theoretically critical cutting depth is 0.25$\mu\textrm{m}$(0.8$\mu\textrm{m}$) in cutting using a square type(V-type) diamond tool that has edge radius of 1$\mu\textrm{m}$(1.5$\mu\textrm{m}$). Experimentally, the dominant cutting mode changes and cutting surface becomes better at critical cutting depth. To get high quality surface, depth of cut must be critical cutting depth because less plastically deformed substrate is left on the surface.

• International Journal of Automotive Technology
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• 제7권6호
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• pp.697-702
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• 2006

The change in the critical speed due to surface temperature of automotive disk brakes may be analyzed both theoretically as well as experimentally. Juddering of disk brakes is closely related to its critical speed. In analyzing the critical speed, if $\sigma$ is positive, Disk develops TEI(Thermo-Elastic Instability) resulting in juddering in disk brakes. And $\sigma$ is affected not only by the critical speed but also by the initial temperature of disk surface. As the initial temperature of the disk surface rises, the critical speed decreases and juddering is developed more easily. Also, when hot spots are developed by TEI, they show large temperature difference in small local range.

• 설비공학논문집
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• 제28권9호
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• pp.373-380
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• 2016

Spray cooling is a technology of increasing interest for electronic cooling and other high heat flux applications. In this study, heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) are measured on a smooth square flat copper heater of $9.53{\times}9.53mm$ at $36^{\circ}C$ in a pool, a smooth flat surface and Thermoexcel-E surfaces are used to see the change in HTCs and CHFs according to the surface characteristics and FC-72 is used as the working fluid. FC-72 fluid has a significant influence on heat transfer characteristics of the spray over the cooling surface. HTCs are taken from $10kW/m^2$ to critical heat flux for all surfaces. Test results with Thermoexcel-E showed that CHFs of all enhanced surface is greatly improved. It can be said that surface form affects heat transfer coefficient and critical heat flux.

• 설비공학논문집
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• 제25권9호
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• pp.522-528
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• 2013

Spray cooling is a technology of increasing interest for electronic cooling and other high heat flux applications. In this study, heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) were measured on a smooth square flat copper heater of $9.53{\times}9.53$ mm at $36^{\circ}C$ in a pool, with a smooth flat surface, and 26 fpi. Low-fin surfaces were used to see the change in HTCs and CHFs according to the surface characteristics, and FC-72 was used as the working fluid. FC-72 fluid had a significant influence on the heat transfer characteristics of the spray over the cooling surface. HTCs were taken from 10 $kW/m^2$ to critical heat flux, for all surfaces. Test results with Low-fin showed that the CHFs of all the enhanced surface were greatly improved. It can be said that the surface form affects the heat transfer coefficient and critical heat flux.

• 한국재료학회지
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• 제19권2호
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• pp.111-114
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• 2009

For the fabrication of core-shell structure bimetallic lead-free solder balls, both the critical temperature ($T_{cr}$) for the phase separation of two immiscible liquid phases and the temperature coefficient of the interfacial tension between the two separated liquid phases are required. In order to obtain this information, the temperature dependence of the surface tension of 60%Bi-24%Cu-16%Sn(-REM) alloys was measured using the constrained drop method. The slope of the temperature dependence of the surface tension changed clearly at a critical temperature for the separation of two immiscible liquid phases. The critical temperature of the 60%Bi-24%Cu-16%Sn alloy was estimated to be 1097K. An addition of 0.05% Ce decreased the critical temperature to 1085K, whereas that of 0.05% La increased it to 1117K. It was found that the surface tension and its temperature coefficient of the 60%Bi-24%Cu-16%Sn alloy were slightly increased by the addition of 0.05% Ce and 0.05% La. In addition, additions of Ce and La increased the temperature coefficient of the interfacial tension.

• 설비공학논문집
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• 제24권9호
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• pp.685-692
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• 2012

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of 5 refrigerants of different vapor pressure are measured on horizontal Thermoexcel-E square surface of 9.53 mm length. Tested refrigerants are R32, R22, R134a, R152a and R245fa. HTCs are taken from 10 $kW/m^2$ to critical heat fluxes for all refrigerant at $7^{\circ}C$. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool. Test results show that critical heat fluxes(CHFs) of Thermoexcel-E enhanced surface are greatly improved as compared to that of a plain surface in all tested refrigerants. CHFs of all refrigerants on the Thermoexcel-E surface are increased up to 100% as compared to that of the plain surface. The improvement of Thermoexcel-E surface in CHF, however, is lower than that of the low fin surface. HTCs on Thermoexcel-E surface increase with heat flux. But after certain heat flux, HTCs began to decrease due to the difficulty in bubble removal caused by the inherent complex nature of this surface. Therefore, at heat fluxes close to the critical one, sudden decrease in HTCs needs to be considered in thermal design with Thermoexcel-E surface.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.774-778
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• 2004

The atomization process of a circular $SF_{6}$ liquid jet issued into an otherwise quiescent, high-pressure $N_2$ gas was observed to explore the breakup mechanism of liquid ligaments involved in turbulent atomization. Both liquid and gas temperatures were fixed at a room temperature but the gas pressure was elevated to more than twice the critical pressure of $SF_{6}$. Therefore, the liquid surface was in a thermodynamic state close to a critical mixing condition with suppressed vaporization. Since the surface tension and the surface gas density approach zero and the surface liquid density, respectively, phenomena equivalent to those which would appear when a very high speed laminar flow of water were injected into the atmospheric-pressure air can be observed by issuing $SF_{6}$ liquid at low speeds in micro-gravity environment which avoid disturbances due to gravity forces. The instability ob near-critical mixing surface jet was quantitatively characterized using a newly developed device, which could issue a very small amount of $SF_{6}$ liquid at small constant velocity into a very high-pressure $N_2$ gas.