• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.847-856
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• 2013

In this study, thermal performance of recuperators with plain and offset strip fins is investigated to enhance the thermal efficiency of a micro gas turbine. Thermal cycle analysis is conducted to determine major design parameters of a single-pass counterflow recuperator. In order to evaluate the performance of the recuperator, the effectiveness and the pressure drop in the recuperators are chosen as the objective function and the design constraint, respectively. The optimized geometries for internal structure of the recuperators with plain and offset strip fins are obtained with varying the fin spacing and height. From the result, the recuperator with offset strip fins has better thermal performance when the fin spacing, s, is smaller than 1.45mm and the thermal performance of the recuperator with plain rectangular fins is higher than that with offset strip fins in the region of $s{\geq}1.45mm$. In addition, it is found that the entrance region effect and the longitudinal wall heat conduction effect should be taken into account for accurately predicting the thermal performance of the recuperators with both plain and offset strip fins.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.30 no.1
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• pp.53-62
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• 2024

Molded pulp products has become more attractive than traditional materials such as expanded polystyrene foam (EPS) owing to low-priced recycled paper, environmental benefits such as biodegradability, and low production cost. In this study, various design factors regarding compression and cushioning characteristics of the molded pulp cushion with truncated pyramid-shaped structural units were analyzed using a test specimen with multiple structural units. The adopted structural factors were the geometric shape, wall thickness, and depth of the structural unit. The relative humidity was set at two levels. We derived the cushion curve model of the target molded pulp cushion using the stress-energy methodology. The coefficient of determination was approximately 0.8, which was lower than that for EPS (0.98). The cushioning performance of the molded pulp cushion was affected more by the structural factors of the structural unit than by the material characteristics. Repeated impacts, higher static stress, and drop height decreased the cushioning performance. Its compression behavior was investigated in four stages: elastic, first buckling, sub-buckling, and densification. It had greater rigidity during initial deformation stages; then, during plastic deformation, the rigidity was greatly reduced. The compression behavior was influenced by structural factors such as the geometric shape and depth of the structural unit and environmental conditions, rather than material properties. The biggest difference in the compression and cushioning characteristics of molded pulp cushion compared to EPS is that it is greatly affected by structural factors, and in addition, strength and resilience are expected to decrease due to humidity and repetitive loads, so future research is needed.

• Journal of the Korean Vacuum Society
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• v.7 no.2
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• pp.118-126
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• 1998

A study to improve filling of semiconductor contact holes by enhancement of the directionality of the source beams has been undertaken. The collimation of source beams was improved by the ionized cluster beam deposition technique with modification of the cell geometry. The collimation tested with neutral beam was excellent. But, the Cu flims were grown in a columnar mode due to the lack of surface mobilit of the impinged clusters. A shadow effect also caused cleavage and consequent discontinuity at the steos as films grow. By applying acceleration voltage, the columnar growth in a contact hole of 0.5 $\mu$m diameter and 1 $\mu$m height disappeared and considerable coverage at the side wall of the contacts as well as perfect bottom coverage were observed. These are all due to the assistants of the accelerated ionized clusters with high kinetic energy. Thus we demonstrated that the ICB deposition technique can be used to completely fill sub-half-micron contact holes with high aspect ratio.

• Journal of the Korean Wood Science and Technology
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• v.45 no.4
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• pp.369-381
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• 2017

The objective of this study was to compare the wood anatomical characteristics of local tree species in Moluccas, Indonesia i.e., Moluccan ironwood (Intsia bijuga), linggua (Pterocarpus indicus), red meranti (Shorea parvifolia), and gofasa (Vitex cofassus). Qualitative evaluation was conducted by observing the anatomical structure in cross, radial, and tangential sections of each sample. For the quantitative evaluation, the dimensions of vessels, rays, and fibers were measured. Qualitative evaluation showed that crystals were observed in Moluccan ironwood, linggua, and gofasa, while resin canals were only observed in red meranti. Tyloses were frequently observed in gofasa but infrequently observed in linggua and red meranti. Quantitative evaluation showed that Moluccan ironwood with the higher density had thicker fiber wall, higher quantity of ray number, and wider rays than the other species. Red meranti had higher values of ray height and fiber length than the other three species. The results also revealed that linggua showed the highest values of relative crystallinity and crystallite width. Red meranti and gofasa showed similar values of relative crystallinity and crystallite width, while Moluccan ironwood showed the lowest values. The basic qualitative and quantitative anatomical characteristics discussed could provide useful information for further utilizations of such wood species.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.571-578
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• 2012

In this paper, an experimental investigation is performed to estimate the thermal performance of a natural convective heat sink with plate fins subject to the uniform wall temperature condition. Extensive experiments are performed with various input powers, fin spacings, and heights of the natural convective heat sinks with plate fins. In particular, the effect of the inclination angle on the thermal performance of the heat sink is studied. In order to validate the experimental data, the experimental results are compared with results from previous studies. Based on the experimental results, the appropriate ranges of the previous correlations between the input power, the fin spacing, the fin height, and the inclination angle for the natural convective heat sink with plate fins are evaluated.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.11-22
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• 2001

The interaction between forward mounted propeller and wing in ground effect, and its aerodynamic performance are analyzed by potential flow approximation. A Vortex Lattice Method(VLM) for the propeller analysis and a potential based panel method for the WIG are used together with an image method by assuming the free surface as a rigid wall. The interaction of propeller and wing in the proximity of the ground is taken into account by an iterative procedure where the boundary conditions are satisfied with the given convergence criteria. The program developed is first checked by comparing its numerical results with the experimental data and other numerical results for the propeller MP101-rudder MR21 system. Then, the propeller-WIG interaction and its performance versus ground clearance are investigated by changing parameters such as propeller position, diameter and speed of revolution. It is shown that the forward mounted propeller increases the lift forces of the wing and also enhances the height stability, depending on the design parameter. Therefore, the appropriate selection of the design parameter such as propeller diameter, revolution, the longitudinal and vertical position of propeller is necessary.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.3
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• pp.183-190
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• 2022

The construction of an underground silo structure was the first stage of erecting the Gyeongju low-and-intermediate-level radioactive waste disposal facility. The facility, completed in 2014, has a scale of 100 000 drums and is currently in operation. The underground silo structure, 25 and 50 m in diameter and height, respectively, consists of cylindrical (for storing waste packages) and dome parts. The dome is divided into lower (connected to the operation tunnel) and upper parts. The wall of the underground silo structure is an approximately 1-m-thick reinforced concrete liner. In this study, finite element analysis was performed for each phase of the construction sequence and operation of the underground silo structure. Two-dimensional axial symmetric finite element analysis was implemented using the SMAP-3D program. Three-dimensional finite element analysis was also performed to examine the reliability of the two-dimensional axial symmetric finite element model. The structural behavior of the underground silo structure was predicted, and its structural safety was examined.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1253-1261
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• 1993

Numerical analysis and measurements of the velocity and temperature distributions in buoyancy assisting laminar mixed convection flow over a vertically located, two-dimensional backward-facing step are reported. Laser-Doppler Velocimeter and Constant Temperature Anemometer operated in constant current were used to measure simultaneously the velocity and temperature distributions in the recirculation region downstream of the step. The reattachment length was measured by using flow visualization technique for different inlet velocities, wall temperatures and step heights. While the reattachment length $X_r$ increases as the inlet velocity or step height increase, it decreases as the buoyancy force increases, causing the size of the recirculation region to decrease. For the experimental range of $Gr_s$/$Re_{s}^{2}$$\times$$10^3$<17, a correlation equation for the reattachment length can be given by $X_{r}=1.05(2.13+0.021 Re_{s})exp$ $(-33.7_s^{-0.186}/Gr_{s}/Re_{s}^2).$ The Nusselt number is found to increase and the location of its maximum value moves closer to the step as the buoyancy force increases. The location of the maximum Nusselt number occurs downstream of the reattachment point, and distance between the reattachment point and the location of the maximum Nusselt mumber increases as the buoyancy force increases. Computational prediction agrees favorably well with measured results.

• Fire Science and Engineering
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• v.19 no.4 s.60
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• pp.69-74
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• 2005

This study is intended to examine the effect of photoluminescent exit signs in the event of failure of both the power to the lighting and illuminated exit sign. To achieve the purpose, the test house was exhibited in Fire EXPO '05. 520 visitors were examined from May 26-29, 2005. The results of this study are as follows; The evacuation from buildings in dark conditions showed that $70\%$ of men and $72\%$ of women were crawled along the wall. Meanwhile, $88\%$ of men and $83\%$ of women were evacuated with ordinary walking in photoluminescent exit signs. The egress time was shortened from 53 seconds to 64 seconds in accordance with age, height and visual power. The photoluminescent exit signs located on public buildings floors will aid in evacuation from buildings in the event of failure of the power to the lightings and illuminated exit signs.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.69 no.1
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• pp.15-24
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• 2024

Environmental factors play an important role in crop growth and development. In recent years, climate change has become a challenge that limits environmental factors. Light is an important environmental factor for photosynthesis in rice. In addition, temperature is one of the most important factors for rice production; thus, a 1℃ increase in temperature because of climate change can affect rice growth and development. Therefore, we investigated the effect of shading on the growth characteristics of rice under different temperature conditions from the vegetative stage to the flowering stage. Plants were grown at three different temperatures: 26℃/16℃ for 21℃, 29℃/19℃ for 24℃, and 22℃/32℃ for 27℃ in a phytotron. A 55% shade treatment was applied after 10 days of transplanting until the flowering stage. Plant height was not affected by the shading treatment. In the maximum tiller number response to shading, a lower tiller number and growth speed of tiller was found in the 27℃ condition. Among leaf characteristics, shading increased the flag leaf area, length, width, and effective leaf area; however, it decreased the leaf number on the main stem, especially at 27℃. In terms of stem characteristics, shading affected culm wall thickness in both varieties. Finally, regarding the panicle characteristics, lower panicle numbers, spikelet numbers per panicle, primary numbers, and secondary numbers per panicle were found under the shading treatment. Most of the desirable characteristics were affected by the shading treatment at 27℃. Overall, these results indicated that shading had a greater effect on rice plant growth at high temperature.