• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1095-1104
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.

• Journal of the Korean Wood Science and Technology
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• v.48 no.4
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• pp.458-471
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• 2020

Effect of pre-treatment and compression ratio on specific gravity (SG) and dimensional stability improvement of three lesser-used wood species from natural forest area of North Kalimantan Province, Indonesia had been investigated. Hot soaking at 80℃ for 3 hours within 2 and 5% of boron solution was applied as pre-treatment, while compression ratio applied was 20 and 40% from the initial thickness. Densification was conducted using hot pressing machine at 30 kg/㎠ of pressure and 160℃ of temperature for 15 minutes. Specific gravity was measured gravimetrically, while dimensional stability was evaluated through thickness swelling and water absorption as the indicator. Results show that SG of densified wood was influenced by wood species and compression ratio, but not by pre-treatment applied; while dimensional stability was influenced by wood species, compression ratio, and pre-treatment. Specific gravity and water absorption of densified wood was improved significantly. Specific gravity increased 28.86-63.03%, while water absorption decreased 12.80-15.89%. Thickness swelling of 20% densified wood was lower than that of 40% densified wood.

• Journal of ILASS-Korea
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• v.15 no.1
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• pp.1-7
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• 2010

As world attention has focused on global warming and air pollution, high efficiency diesel engines with low $CO_2$ emissions have become more attractive. Premixed diesel engines in particular have the potential to achieve the more homogeneous mixture in the cylinder which results in lower NOx and soot emission. Early studies have shown that the operation conditions such as the EGR, intake conditions, injection conditions and compression ratio are important to reduce emissions in a PCCI (Premixed Charge Compression Ignition) engine. In this study a modified cam was employed to reduce the effective compression ratio. While opening timing of the intake valve was fixed, closing timing of the intake valve was retarded $30^{\circ}$. Although Atkinson cycle with the retarded cam leads to a low in-cylinder pressure in the compression stroke, the engine work can still be increased by advanced injection timing. On that account, we investigated the effects of various injection parameters to reduce emission and fuel consumption; as a result, lower NOx emission levels and almost same levels of fuel consumption and PM compared with those of conventional diesel engine cam timing could be achieved with the LIVC system.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.435-438
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• 2008

High temperature deformation of Ti-6Al-4V alloy with a lamellar colony microstructure was investigated by hot compression and torsion tests. The torsion and compression tests were carried out under a wide range of temperatures and strain rates with true strain up to 2 and 0.7, respectively. The processing maps were generated on the basis of compression and torsion test data and using the principles of dynamic materials modeling (DMM). The shapes of the strain-stress curves in alpha-beta region and processing maps obtained on the two different tests have been compared with a view to evaluate the effect of the microstructure evolution on the flow softening behavior of Ti-6Al-4V alloy with a lamellar colony microstructure.

• Fashion & Textile Research Journal
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• v.21 no.2
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• pp.209-219
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• 2019

This study analyzed and compared wearer mobility for different types of clothing that also included the potential to develop firefighter station uniforms using range of motion (ROM) and electromyography (EMG). This study focused on a comparison of wearer mobility affected by different materials and shapes of the station uniforms worn under firefighter turnout gear. Japanese standard uniform (UNI), stretch-wear (ST), and compression-wear (CP) were used as station uniforms for the experiment. This study analyzed wearer movements and quantified ROM and EMG. In addition, the subjective evaluation of wearer mobility and comfort were assessed for comparisons. Nine healthy male students participated in the experiment. Wearer mobility was analyzed using ROM and EMG data obtained by measuring five motions; in addition, subjective evaluations were also obtained. As compared with the standard station uniform, ROM increased 6.8 % and 7.2 % due to stretch-wear and compression-wear. The benefits of wearing stretch material or compression material to improve muscle performance (such as reduced percent of maximum voluntary contraction) were not proven. Differences between materials and designs influenced subjective wearer comfort. In particular, the wearing of compression materials was shown best in terms of wearer comfort that may also allow greater wearer mobility.

• Structural Engineering and Mechanics
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• v.71 no.3
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• pp.211-221
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• 2019

To study the eccentric compression behavior of ultra-high performance fiber reinforced concrete (UHPFRC) columns, six UHPFRC columns and one high-strength concrete (HSC) column were tested. Variation parameters include load eccentricity, volume of steel fibers and stirrup ratio. The crack pattern, failure mode, bearing capacity, and deformation of the specimens were studied. The results showed that the UHPFRC columns had different failure modes. The large eccentric compression failure mode was the longitudinal tensile reinforcements yielded and many horizontal cracks appeared in the tension zone. The small eccentric compression failure mode was the longitudinal compressive reinforcements yielded and vertical cracks appeared in the compressive zone. Because of the bridging effect of steel fibers, the number of cracks significantly increased, and the width of cracks decreased. The load-deflection curves of the UHPFRC columns showed gradually descending without sudden dropping, indicating that the specimens had better deformation. The finite element (FE) analysis was performed to stimulate the damage process of the specimens with monotonic loading. The concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC. The contribution of the UHPFRC tensile strength was considered in the bearing capacity, and the theoretical calculation formulas were derived. The theoretical calculation results were consistent with the test results. This research can provide the experimental and theoretical basis for UHPFRC columns in engineering applications.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.101-109
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• 2008

In order to investigate the influence of the water on compression characteristic of decomposed granite soils, a single particle crushing test and one-dimensional compression tests were carried out on three decomposed granite soils and Silica sand. The initial fracture strength for single particle reduced and variability of the strength increases due to weakening by existing water. Moreover, it was recognized that one-dimensional compression characteristic was related to the initial fracture strength characteristic, and the initial fracture strength also has the effect of weathering.

• ETRI Journal
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• v.46 no.3
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• pp.538-549
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• 2024

A conventional codec aims to increase the compression efficiency for transmission and storage while maintaining video quality. However, as the number of platforms using machine vision rapidly increases, a codec that increases the compression efficiency and maintains the accuracy of machine vision tasks must be devised. Hence, the Moving Picture Experts Group created a standardization process for video coding for machines (VCM) to reduce bitrates while maintaining the accuracy of machine vision tasks. In particular, in-loop filters have been developed for improving the subjective quality and machine vision task accuracy. However, the high computational complexity of in-loop filters limits the development of a high-performance VCM architecture. We analyze the effect of an in-loop filter on the VCM performance and propose a suboptimal VCM method based on the selective activation of in-loop filters. The proposed method reduces the computation time for video coding by approximately 5% when using the enhanced compression model and 2% when employing a Versatile Video Coding test model while maintaining the machine vision accuracy and compression efficiency of the VCM architecture.

• Journal of the Korean Society of Industry Convergence
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• v.14 no.4
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• pp.143-149
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• 2011

The experiment has been investigated the room temperature change under adjusting 4-way valve which was installed for cooling and heating switch. Beside, the temperature of heat pump was controlled automatically for autonomously adjusting temperature and maintaining a constant room temperature. As results, Inlet & outlet temperature differences of compressor are $95^{\circ}C$ in cooling condition and $57^{\circ}C$ in heating condition. Therefore, Compression efficiency of cooling effect is higher than heating effect. In addition, Heat exchange effect of Cooling system condition is higher than heating system. This results can be used for studying about automatic temperature control of cooling and heating system with heat pump and 4way valve.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.264-267
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• 2004

It is well known that axial tension decreases the shear strength of RC beams without transverse reinforcement, and axial compression increases the shear resistance. What is perhaps not very well understood is how much the shear capacity is influenced by axial load. RC beams without shear reinforcement subjected to large axial compression and shear may fail in a very brittle manner at the instance of first diagonal cracking. As a result, a conservative approach should be used for such members. According to the ACI Code, the concrete contribution is calculated by effect of axial force and the vertical force in the stirrups calculated by $45^{\circ}$ truss model. This study was performed to examine the effect of axial force in reinforced concrete beams.