• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.79-93
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• 2013

One of the biggest problems affecting bridges is the transverse cracking and deterioration of concrete bridge decks. The causes of early age cracking are primarily attributed to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. The cracks can be influenced by material characteristics, casting sequence, formwork, climate conditions, geometry, and time dependent factors. The cracking of bridge decks not only creates unsightly aesthetic condition but also greatly reduces durability. It leads to a loss of functionality, loss of stiffness, and ultimately loss of structural safety. This investigation consists of field, laboratory, and analytical phases. The experimental and field testing investigate the early age transverse cracking of bridge decks and evaluate the use of sealant materials. The research identifies suitable materials, for crack sealing, with an ability to span cracks of various widths and to achieve performance criteria such as penetration depth, bond strength, and elongation. This paper also analytically examines the effect of a wide range of parameters on the development of cracking such as the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits liveload deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. The deflection is found to be an important parameter to affect cracking. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.2
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• pp.59-64
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• 2014

Cu-Al-Mn shape memory alloys of a variety of composition were characterized in terms of shape memory properties and cold workability. Cold workability tested by cold rolling indicated that the alloys solution treated in the ${\alpha}+{\beta}$ region have a higher ductility than those solution treated in the ${\beta}$ region. Also it is known that cold workability increased with the decrease in Al content in the ${\beta}$ region. This seems to be resulted from the fact that Mn addition causes to expand ${\beta}$ region toward lower Al content and lower order-disorder transition temperature, consequently, ${\beta}$ of excellent workability being frozen even at room temperature. Experimental results regarding shape memory showed that the properties were better with a higher Al contents at a given Mn content, which is closely related with martensitic transformation. It is also shown that super elasticity limit was enhanced with decrease in the yield strength of alloys because a lower yield strength seems to initiates slip at the lower applied stress.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.2
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• pp.43-53
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• 1989

In this research programs, a series test was conducted to show the effects of freeze/thaw process on the various soil properties. The tests were carried out taken from the west sea shore of Korean peninsular and the west sea shore of Scotland, and their results are as follows; 1. There was a positive total heave in a freezing run, although water may he expelled for the sample initially. The water flow must he reverse' from expulsion to intake. 2. The confining pressure had an overriding influence on the heave and frost penetration, a sudden change of the axial strain at failure with strain rate was observed occuring at a strain rate between 10-5 and 10-6, and the initial friction angle of frozen clay was appeared zero. 3. There was shown a significant decrease in liquid limit of soil which was subjected to freeze/thaw process for the initial value of about 20% because of soil particles aggregation. 4. The cyclic freeze/thaw caused a sinificant reduction in shear strength and its thixotropic regain. The frozen/thawed soil exibited negative strength regain, particularly at high freeze/thaw cycles. 5. The freezing temperature greatly influenced on the failure strength of soils and this. Trend was more pronounced the lower the freezing temperature and shown the ductile failure with indistinct peaks.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.1
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• pp.33-38
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• 2010

Developments of numerical methods are very important to design and analysis for a high subsonic turbine blade. In general, Analysis by experimental investigation has needed a lot of human resources and required time, indispensably, and equipments still have a limit to measure in conditions of high temperature. Rapid technological developments of CPU and integration level of memory make it possible to advance computation with almost exactly simulation so, recent developments of numerical methods are in spotlight. In the present study, the panel method, which is well-known as relatively simplified numerical method, and 2-dimensional ordinary differential Falkner-Skan equation were computed in order to analyze the outer flow, and FVM-based solid heat transfer equation, was also computed to forecast the temperature distribution of the airfoil and the turbine blade. Unstructured grid was constructed in the turbine blade, which has double cooling holes, in order to analyze the internal heat transfer. Cooling fluid was assumed as fully-developed turbulent flow and that circulated in cooling holes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.12
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• pp.852-858
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• 2010

In an absorption chiller, solution is circulated by a solution pump with an inverter to vary flow rate depending on operating conditions. For optimal operation, the solution level in the high temperature generator should be kept constant. However, a sensor for measuring continuous level is not available because of varying solution concentration. Instead, level switches are used and hence feedforward control associated with limit checking is a common practice. In the study, inverter frequencies are estimated from a dynamic simulation model and pump performance. Designed frequencies are compared with those implemented in real chillers. It was found that the frequencies used in real chillers are larger than those needed in circulation flow rates. It was intended to prevent system shut-off caused by dry-out. However, it is necessary to minimize the excessive frequency setting in order to reduce frequent pump stops and the range of solution level for continuous pump operation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.6
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• pp.29-35
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• 2005

This paper presents the basic quench protection idea for the HTS(High-Temperature Superconducting) cable. In Korea power system, the transfer capability of transmission line is limited by the voltage stability, HTS cable could be one of the countermeasure to enhance the transfer limit with its higher current capacity and lower impedance[1]. However, the quench characteristic makes not only HTS cable to loss its superconductivity, but also change the impedance of the transmission line and power system operating condition dramatically. This pheonominum threats HTS cable safety as well as power system security, therefore a proper protection scheme and security control counterplan have to be established before HTS cable implementation. In this paper, the quench characteristics of HTS cable for the fault current based on heat balance equation was established and a proper protection method regarding conventional protection system was suggested.

• Atmosphere
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• v.25 no.2
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• pp.193-203
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• 2015

A large aperture scintillometer (LAS) was deployed with an optical path length of 2.1 km to estimate turbulent sensible heat flux (${\mathcal{Q}}_H$) over a highly heterogeneous urban area. Scintillation measurements were conducted during cold season in November and December 2013, and the daytime data of 14 days were used in the analysis after quality control processes. The LAS-derived ${\mathcal{Q}}_H$ show reasonable temporal variation ranging $20{\sim}160W\;m^{-2}$ in unstable atmospheric conditions, and well compare with the measured net radiation. The LAS footprint analysis suggests that ${\mathcal{Q}}_H$ can be relatively high when the newly built-up urban area has high source contribution of the turbulent flux in the study area ('northwesterly winds'). Sensitivity tests show that the LAS-derived ${\mathcal{Q}}_H$ are highly sensitive to non-dimensional similarity function for temperature structure function parameter, but relatively less sensitive to surface aerodynamic parameters and meteorological variables (temperature and wind speed). A lower Bowen ratio also has a significant influence on the flux estimation. Overall uncertainty of the estimated daytime ${\mathcal{Q}}_H$ is expected within about 20% at an upper limit for the analysis data. It is also found that stable atmospheric conditions can be poorly determined when the scintillometry technique is applied over the highly heterogeneous urban area.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.218-224
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• 2003

This paper describes a novel MEMS integration technique on a CMOS chip. MEMS integration on CMOS circuit has many advantages in view of manufacturing cost and reliability. The surface topography of a CMOS chip from a commercial foundry has 0.9 ${\mu}{\textrm}{m}$ bumps due to the conformal coating on aluminum interconnect patterns, which are used for addressing each MEMS element individually. Therefore, it is necessary to achieve a flat mirror-like CMOS chip fer the microelectromechanical system (MEMS) such as micro mirror array. Such CMOS chip needs an additional thickness of the dielectric passivation layer to ease the subsequent planarization process. To overcome a temperature limit from the aluminum thermal degradation, this study uses RF sputtering of silicon nitride at low temperature and then polishes the CMOS chip together with the surrounding dummy pieces to define a polishing plane. Planarization reduces 0.9 ${\mu}{\textrm}{m}$ of the bumps to less than 25 nm.

• Food Science and Biotechnology
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• v.18 no.4
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• pp.895-899
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• 2009

A new approach for the determination of acrylamide (AM) in foods by solid phase microextraction-gas chromatography (SPME-GC) was established. AM was bromized and transformed to 2-bromoacrylamide (2-BAM). 2-BAM was then extracted by a commercial SPME fiber, $75-{\mu}m$ Car/PDMS fiber, for GC detection. The influence of extraction and desorption parameters such as extraction temperature and time, stirring rate, desorption temperature, and time were studied and optimized. The mass concentration was proportional to the peak area of 2-BPA from 1.0 to 8,000 ${\mu}g/L$. The detection limit of the SPME-GC for 2-BAM was found to be 0.1 ${\mu}g/L$, and the recoveries and relative standard deviations for different food samples were 74.5 to 102.0%, and 4.2 to 9.1%, respectively. The presented method was applied to the determination of AM in fried foods.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.261-261
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• 1999

We observed leveling-off of the resistance in granular In/InO$_x$ thin films in the zero-temperature limit. The temperature T$_b$ at which the leveling-off appears gets larger as the sheet resistance R$_n$ increases. This is consistent with the concept that the leveling-off of the resistance is due to the dissipation of the bosonic phase and that the dissipation is enhanced as the resistance increases. The magnetic field dependence of the saturated resistance R$_b$ at low temperatures fits the modified square-root cusp-like form R$_b$/R$_n$=α exp[-b(B/B$_c$-1)$^{-1/2}$] for the magnetic field in the range B$_c$$_f$ where B$_c$ is the onset magnetic field of the resistance leveling-off. α and b are constants of order 1. For B>B$_f$ tansport properties are described by the theory of the fermi insulator. From the results, we attribute the leveling-off to the dissipative quantum tunneling of vortices, which supports the models predicting the vortex-motion-induced insulating phase related with the concept like"dirty boson" [1]l and "hose metal" [2].