• Journal of the Korea Convergence Society
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• v.12 no.11
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• pp.81-90
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• 2021

There are various optimization problems in real world and research continues to solve them. An optimization problem is the problem of finding a combination of parameters that maximizes or minimizes the objective function. Harmony search is a population-based metaheuristic algorithm for solving optimization problems and it is designed to mimic the improvisation of jazz music. Harmony search has been actively applied to optimization problems in various fields such as civil engineering, computer science, energy, medical science, and water quality engineering. Harmony search has a simple working principle and it has the advantage of finding good solutions quickly in constrained optimization problems. Especially there are various application cases showing high accuracy with a low number of iterations by improving the solution through the empirical derivative. In this paper, we explain working principle of Harmony search and classify the leading research in recent 3 years, review them according to category, and suggest future research directions. The research is divided into review by field, algorithmic analysis and theory, and application to real world problems. Application to real world problems is classified according to the purpose of optimization and whether or not they are hybridized with other metaheuristic algorithms.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.829-838
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• 2022

This study conducts Hypervelocity Impact(HVI) simulations considering space objects with various shapes and different impact angles. A commercial nonlinear structural dynamics analysis code, LS-DYNA, is used for the present simulation study. The Smoothed Particle Hydrodynamic(SPH) method is applied to represent the impact phenomena with hypervelocity. Mie-Grüneisen Equation of State and Johnson-Cook material model are used to consider nonlinear structural behaviors of metallic materials. The space objects with various shapes are modeled as a sphere, cube, cylinder, and cone, respectively. The space structure is modeled as a thin plate(200 mm×200 mm×2 mm). HVI simulations are conducted when space objects with various shapes with 4.119 km/s collide with the space structures, and the impact phenomena such as a debris cloud are analyzed considering the space objects with various shapes having the same mass at the different impact angles of 0°, 30° and 45° between the space object and space structure. Although space objects have the same kinetic energy, different debris clouds are generated due to different shapes. In addition, it is investigated that the size of the debris cloud is decreased by impact angles.

• Industry Promotion Research
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• v.7 no.3
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• pp.103-113
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• 2022

In this study, in the Nativity birth chart of Classic Astrology, the study was conducted under the premise that 'If the natives are born with different structures to govern their diseases, diseases may appear differently in the lives of natives.' did. In the birth chart, an individual's innate health was analyzed through the strengths and weaknesses of sign, planets, and aspects. In the case of managing congenital diseases, we studied the aspect relationship between the native's ASC constellation and the fixed star and planet in the Nativity Birth Chart. In the case of controlling acquired diseases, it was judged by examining the constellations, rulers, and planets of the 6^th house that control diseases in the Nativity birth chart. In the case of acquired diseases, natives may be exposed to various accidents and diseases throughout their lives. So, we looked at the relationship between diseases through the energy and weakness of the planet coming through Pirdaria, the aspect relationship with the planet, and fixed star. As a result of the study, a native's health status is given differently depending on the strength and weakness of the innate sign and planet in the Nativity Birth Chart. And it has been proven that the health of the native is determined by the state of the 6^th House, who rules over disease, and the disease and accidents that come from Direction are determined by the relationship between the planet and the aspect coming from Pirdaria.

• Journal of Aerospace System Engineering
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• v.17 no.1
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• pp.42-50
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• 2023

In this study, hexagonal ferrite powder with chemical formula SrZn_2-xCo_xFe₁₆O₂₇ was synthesized by a solid-state reaction method and its electromagnetic (EM) wave absorption characteristics were evaluated in the frequency range of 0.1-18 GHz with absorber thickness range of 0 - 10 mm. Reflection loss (RL) affecting electromagnetic wave absorption performance was calculated based on the transmission line theory using measured complex permeabilities and permittivities. RL spectra were also directly measured for some samples. They were well matched with calculated results. High-frequency complex permeability characteristics were changed gradually according to the amount of Co substitution (x). The EM wave absorption frequency band could be tuned accordingly. Hexaferrite samples with x = 1.0, 1.25, and 1.5 exhibited remarkable maximum electromagnetic wave absorption performances with minimum RL (RL_min) lowered than -50 dB. They also showed a very broad frequency band (Δf > 10 GHz) in which more than 90% of the EM wave energy absorption occurred (RL ≤ -10 dB).

• Korean Journal of Poultry Science
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• v.14 no.1
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• pp.9-13
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• 1987

Three-week-old, broiler-type, mixed sex chicks were divided into replicate groups of 10 birds each and fed for 5 weeks. The wheat bran was defatted and added at 0, 10 and 20% levels. A fourth group received the 20% wheat bran plus a cellulase enzyme added at the level of 0.008%. After a five-week experimental period without a marker a 24-pen battery on the four diets were supplemented with 1% chromic oxide and fed 100g daily. After a 2-day preliminary period, feces were collected three times daily from each diet group for two days at 2, 4 or 8 hours after feeding. At the end of 4 days, within each diet group, birds were randomly selected for slaughter at 2, 4 or 8 hours after feeding and the entire gastrointestinal tract was removed and ligated to form five compartments. The lengths of each segment were measured after straightening, and the gizzard was emptied and weighed. The summarized data showed that the group fed on the high-energy basal diet had the lowest gizzard weight (P〈0.05). Chromium turnover time (minutes) in the each segment and entire GI tract of chicks was not influenced by the high fiber diet or cellulase.

• Journal of the Korean Magnetics Society
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• v.3 no.1
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• pp.48-55
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• 1993

We report the photoemission (PES) studies for the Co/Pd multilayter. The Co 3d PES spectrum of Co/Pd exhibits two interesting features, one near the Fermi energy, $E_{F}$, and another at ~2.5 eV below $E_{F}$. The Co 3d peak near $E_{F}$ of Co/Pd is much narrower than that of the bulk Co, consistent with the enhanced Co magnetic moment in Co/Pd compared to that in the bulk Co. The Co 3d feature at ~-2.5 eV resembles the Pd valence band structures, which suggests a substantial hybridization between the Co and Pd sublayers. The Co 3d PES spectrum of Co/Pd is compared with the existing band structures, obtained using the local spin density functional calculations. A reasonable agreement is found concerning the bandwidth of the occupied part of the Co 3d band, whereas a narrow Co 3d peak near $E_{F}$ seems not to be described by the band structure calculations.

• Journal of the Korean Electrochemical Society
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• v.26 no.4
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• pp.43-55
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• 2023

Mass transport through nanoporous structures such as nanopores or nanochannels has fundamental electrochemical implications and many potential applications as well. These structures can be particularly useful for water treatment, energy conversion, biosensing, and controlled delivery of substances. Earlier research focused on creating nanopores with diameters ranging from tens to hundreds of nanometers that can selectively transport cationic or anionic charged species. However, recent studies have shown that nanopores with diameters of a few nanometers or even less can achieve more complex and versatile transport control. For example, nanopores that mimic biological channels can be functionalized with specific receptors to detect viruses, small molecules, and even ions, or can be made hydrophobic and responsive to external stimuli, such as light and electric field, to act as efficient valves. This review summarizes the latest developments in nanopore-based systems that can control mass transport based on the size of the nanopores (e.g., length, diameter, and shape) and the physical/chemical properties of their inner surfaces. It also provides some examples of practical applications of these systems.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.517-522
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• 2023

A chemical/mechanical durability test of polymer membrane evaluation method is used in which air and hydrogen are supplied to the proton exchange membrane fuel cell (PEMFC) and wet/dry is repeated in the open circuit voltage (OCV) state. In this protocol, when wet/dry is repeated, voltage increase/decrease is repeated, resulting in electrode degradation. When the membrane durability is excellent, the number of voltage changes increases and the evaluation is terminated due to electrode degradation, which may cause a problem that the original purpose of membrane durability evaluation cannot be performed. In this study, the same protocol as the department of energy (DOE) was used, but oxygen was used instead of air as the cathode gas, and the wet/dry time and flow rate were also increased to increase the chemical/mechanical degradation rate of the membrane, thereby shortening the durability evaluation time of the membrane to improve these problems. The durability test of the Nafion 211 membrane electrode assembly (MEA) was completed after 2,300 cycles by increasing the acceleration by 2.6 times using oxygen instead of air. This protocol also accelerated degradation of the membrane and accelerated degradation of the electrode catalyst, which also had the advantage of simultaneously evaluating the durability of the membrane and the electrode.

• Steel and Composite Structures
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• v.49 no.2
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• pp.245-255
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• 2023

The present paper summarizes the results of an experimental program on the influence of using waste lathe scraps in the concrete mixture on the shear behavior of RC beams with different amounts of shear reinforcement. Three different volumetric ratios (1, 2 and %3) for the scraps and three different stirrup spacings (160, 200 and 270 mm) were adopted in the tests. The shear span-to-depth ratios of the beams were 2.67 and the stirrup spacing exceeded the maximum spacing limit in the building codes to unfold the contribution of lathe scraps to the shear resistances of shear-deficient beams, subject to shear-dominated failure (shear-tension). The experiments depicted that the lathe scraps have a pronounced contribution to the shear strength and load-deflection behavior of RC beams with widely-spaced stirrups. Namely, with the addition of 1%, 2% and 3% waste lathe scraps, the load-bearing capacity escalated by 9.1%, 21.8% and 32.8%, respectively, compared to the reference beam. On the other hand, the contribution of the lathe scraps to the load capacity decreases with decreasing stirrup spacing, since the closely-spaced stirrups bear the shear stresses and render the contribution of the scraps to shear resistance insignificant. The load capacity, deformation ductility index (DDI) and modulus of toughness (MOT) values of the beams were shown to increase with the volumetric fraction of scraps if the stirrups are spaced at about two times the beam depth. For the specimens with a stirrup spacing of about the beam depth, the scraps were found to have no considerable contribution to the load capacity and the deformation capacity beyond the ultimate load. In other words, for lathe scrap contents of 1-3%, the DDI values increased by 5-23% and the MOT values by 63.5-165% with respect to the reference beam with a stirrup spacing of 270 mm. The influence of the lathe scraps to the DDI and MOT values were rather limited and even sometimes negative for the stirrup spacing values of 160 and 200 mm.

• Clean Technology
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• v.29 no.4
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• pp.244-248
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• 2023

Recently, displays play an important role in quickly delivering a lot of information. Research is underway to reproduce various colors close to natural colors. In particular, research is being conducted on the light emitting structure of displays as a method of expressing accurate and rich colors. Due to the advancement of technology and the miniaturization of devices, the need for small but high visibility displays with high efficiency in energy consumption continues to increase. Efforts are being made in various ways to improve OLED efficiency, such as improving carrier injection, structuring devices that can efficiently recombine electrons and holes in a numerical balance, and developing materials with high luminous efficiency. In this study, the electrical and optical properties of the seven-layer stacked structure rear-light emitting blue OLED device were analyzed. 4,4'-Bis(carazol-9-yl)biphenyl:Ir(difppy)2(pic), a blue light emitting material that is easy to manufacture and can be highly efficient and brightened, was used. OLED device manufacturing was performed via the in-situ method in a high vacuum state of 5×10-8 Torr or less using a Sunicel Plus 200 system. The experiment was conducted with a seven-layer structure in which an electron or hole blocking layer (EBL or HBL) was added to a five-layer structure in which an electron or hole injection layer (EIL or HIL) or an electron or hole transport layer (ETL or HTL) was added. Analysis of the electrical and optical properties showed that the device that prevented color diffusion by inserting an EBL layer and a HBL layer showed excellent color purity. The results of this study are expected to greatly contribute to the R&D foundation and practical use of blue OLED display devices.