Our study experimentally evaluates the structural characteristics of a Cone-Shaped Friction Isolator (CFI) as part of research on sliding bearings. With its relatively simple configuration and effective restoring mechanism, the CFI has significant practical implications for structural engineering. We designed the shape and components of the CFI, and its operation and restoring mechanisms were theoretically reviewed. A prototype of the CFI was developed, and structural characteristic experiments were conducted, focusing on design parameters such as the cone’s inclination angle, the friction coefficient of the contact surface, the magnitude of the vertical load applied to the isolator, and the horizontal loading frequency. The experimental results provide valuable insights into the structural characteristics of devices in terms of critical shear force and restoring shear force.

풀빅산(FA)은 Fe(III)을 킬레이트화하여 생물학적으로 이용 가능한 Fe(II)로 전환함으로써 대형 해조류의 성장을 촉진하고 손 상된 해중림의 복원을 돕는다. 이에 본 연구에서는 풀빅산의 공급에 따른해중림 개선에 미치는 효과를 조사, 분석하였다. FA 보충제는 철(Fe) 부족 해역 내 인공 어초에 설치되었으며, 해조류 군집 및 해양 환경조사는 사계절을 대표하는 학술 잠수를 통해 수행되었다. 연 구 결과, 풀빅산 공급으로 인해 가용 철(Fe) 농도가 증가하면서 해조류의 광합성과 영양소 흡수가 촉진되어 성장률이 향상되는 것으로 나타났다. 우점종의 총 생물량은 전체 해조류 총 생물량과 비우점종에 비해 더욱 강한 상관관계를 나타내었다. 이는 철 보충제가 특정 우점종의 양적 증가에 기여하며, FA 보충제가 설치된 어초에서 해조류 군집의 양적 및 구조적 변화를 유발했음을 시사한다. 본 연구 결과는 풀빅산을 해중림 복원에 적용하기 위한 기초적인 정보를 제공하며, 향후 해조류 생태계 관리 및 보존 전략 수립에 기여할 수 있을 것으로 기대된다.

Most reinforced concrete (RC) school buildings constructed in the 1980s have seismic vulnerabilities due to low transverse reinforcement ratios in columns and beam-column joints. In addition, the building structures designed for only gravity loads have the weak-columnstrong- beam (WCSB) system, resulting in low lateral resistance capacity. This study aims to investigate the lateral resistance capacities of a two-story, full-scale school building specimen through cyclic loading tests. Based on the experimental responses, load-displacement hysteresis behavior and story drift-strain relationship were mainly investigated by comparing the responses to code-defined story drift limits. The test specimen experienced stress concentration at the bottom of the first story columns and shear failure at the beam-column joints with strength degradation and bond failure observed at the life safety level specified in the code-defined drift limits for RC moment frames with seismic details. This indicates that the seismically vulnerable school building test specimen does not meet the minimum performance requirements under a 1,400-year return period earthquake, suggesting that seismic retrofitting is necessary.

This paper aims to quantify the retrofit effect of the Bolt Prefabricated Concrete-Filled Tube reinforcement method on non-seismic school reinforced concrete building through static cyclic loading experiments. To achieve the objective, two-story specimens including a non-retrofitted frame(NRF) and a Bolt Prefabricated Concrete-Filled Tube Reinforcement Frame(BCRF) were tested under static cyclic loading, and the lateral resistant capacities were compared in terms of maximum strength, initial stiffness, effective stiffness, and total energy dissipation. In addition, the load-displacement curves were compared to the story drift limit specified in Seismic Performance Evaluation and Retrofit Manual for School Facilities to investigate if the retrofitted frame was satisfied in target performance(life safety). Experimental results showed that BCRF successfully met the target performance, with a 200% increase in maximum strength and a 300% increase in energy dissipation capacity. Additionally, both initial stiffness and effective stiffness improved by more than 30% compared to NRF. Furthermore, BCRF exhibited an effect that delayed the occurrence of bond failure.

In this study, the initial operation characteristics of a multi-type cooling system with three indoor units using an inverter compressor were investigated experimentally using a calorimeter. The operating characteristics of the cooling system were confirmed under the full load condition of simultaneous operation of three rooms and the partial load condition of individual operation of two or one room under the standard cooling conditions. The capacities of A, B and C are 50, 20, and 30% of the total capacity, respectively. The 3 room combination has 100% capacity, the 2 room combination has 50, 70 and 80% capacity, and the 1 room has 20, 30, and 50% capacity. The compressor condensing and evaporating pressures, the electronic expansion valve openings of indoor units A, B, and C, and the compressor operating frequencies were measured for 10 minutes after the cooling system was started. During the initial operation, the changes in the operating time and opening of the electronic expansion valve varied depending on the indoor unit combination and the operating load, and the relationship between the compressor pressure and the operating frequency was found.

For experimental studies on the production of MR fluid for MR dampers, MR fluid with a viscosity of 506 cP and a density of 2.6 g/cc was produced. In order for MR fluid to have suitable performance for MR dampers, it is important to select surfactants, magnetic particles, base oil, and characteristic additives to obtain high damping force and maintain physical and chemical properties. In order to investigate the redispersibility of MR fluid, viscosity, density, saturation magnetic flux density, dispersibility, and temperature effects were evaluated. A particle size distribution meter and a vibrating magnetometer were used, and a yield stress and redispersion device were developed to obtain the yield stress of the MR fluid. The recovery rate of MR fluid was approximately 97% at 0.2% succinic acid coating and 8% anti-settling agent. And when current is applied, the viscosity increases by more than 90% due to magnetic properties.

일반적으로 전기 패널은 용접이나 앵커링을 통해 기초에 설치된다. 콘크리트 기초-앵커 시스템에서 고려해야 할 열화 요인에 는 콘크리트 기초의 균열이 포함된다. 콘크리트 균열은 전기 패널의 앵커에 영향을 미치는 열화 현상 중 하나로 간주될 수 있다. 또한 독립반 및 열반된 전기 패널의 동적 특성은 상당히 다를 수 있다. 그러나 많은 연구자들이 하나의 전기 캐비닛 시편으로 진동대실험을 수행하였다. 따라서 열반 구성을 고려하여 동적 특성을 평가할 필요가 있다. 본 연구에서는 0.5 mm 및 1.0 mm 균열 폭을 고려하여 콘크리트 기초-앵커 시스템을 설계하였다. 콘크리트 기초-앵커 시스템을 진동대에 고정하고 1∼3개의 열반으로 구성된 단순화된 캐비 닛 모델을 설치하였다. 열반 수와 콘크리트 균열을 매개변수로 고려하여 진동대에 의한 공진주파수 검색 실험을 수행했으며 각 실험편 의 공진 주파수를 비교하였다.

The heat transfer characteristics of double-pipe spiral heat exchanger using aluminum oxide nano-fluid were investigated by three different sizes of curvature size, experimentally. Five concentration of nano-fluid as working fluid were made and tested to analyze the heat transfer characteristics. As results, the heat transfer performance was improved at 0.25% of nano-fluid due to high thermal conductivity, however, as the concentration of nanofluid increased (~2.0%), the heat transfer performance deteriorated due to the increase in thermal resistance caused by the sedimentation of particles in the flow path. In addition, the nano-fluid has a higher pressure drop than water due to its high density and viscosity. The optimal range for heat transfer enhancement of nano-fluid was found to be less than 4.0 LPM in flow rate and 0.25% of nano-fluid concentration in this study.

This study analyzed the epilithic diatom community and ecological health of freshwater streams using environmental DNA (eDNA)-based metabarcoding technology. eDNA metabarcoding is a method that analyzes biological communities by performing PCR amplification followed by next-generation sequencing (NGS), offering higher sensitivity and faster results compared to traditional microscopic analyses. The study compared the eDNA metabarcoding results of ribulose bisphosphate carboxylase large chain gene (rbcL) targeting epilithic diatoms according to Taq polymerases (SuperFi II, GainBlue, EzPCR, and AccuPower). SuperFi II and GainBlue yielded the highest number of reads and zOTUs, with GainBlue showing particularly uniform read distribution, allowing for more accurate analysis for community diversity of epilithic diatoms. On the other hand, EzPCR and AccuPower exhibited lower number of reads and zOTUs, making them less suitable for the community diversity. In terms of community similarity analysis, SuperFi II and GainBlue produced highly similar results, while EzPCR and AccuPower showed significant differences. This study demonstrates that PCR Taq polymerases significantly influence community diversity and similarity analyses of epilithic diatoms, with GainBlue providing the most stable and accurate results. Our findings serve as a valuable foundation for improving the accuracy of eDNA-based metabarcoding analyses of diatoms.

본 연구는 암순응(Dark adaptation)은 인간이 어두운 환경에 적응하는 과정으로, 시각 시스템 이 저조도 환경에서의 시각 정보를 처리하는 능력을 향상시키기 위해 필요하다. 암순응 현상은 야간작업 및 실내작업 등에서 교통사고, 넘어짐 등 작업자의 안전에 영향을 미치며, 조도의 급격한 변화에 따른 개인의 시각적 인지능력의 차이를 이해하는 것은 사고의 예방을 위한 조치에 중요한 요소가 된다. 연구에서는 개인의 시각적 인지에 따른 뇌파 변화를 측정하여 안전거리 확보, 반사광 활용 등 안전사고를 예방하기 위한 영향요인에 대한 기초자료를 제공하므로서 기업의 안전경영을 돕고자 한다. 연구는 암순응 상태의 밝은 조도(Bright Light, BL) 150 lux, 어두운 조도(Dark Light, DL) 4 lux에서 RL-GR(Reflected Light-GReen, Hex code : #D9FF00) 반사광의 거리 3m, 5m, 7m에 따라 뇌파 특성(인지능력)을 뇌파 측정기QEEG-64FX (LAXTHA, Korea) 로 분석하였다. 실험 결과, 사건 관련 전위 (Event-Realated Potential, ERP) 인지 분석을 통하여, RL-GR 반사광의 3m 거리에서 인지 반응 시간(Reaction Time)이 가장 빠른(평균 300ms) 반응이 나타났으며, 이는 인지 처리 능력이 우수함을 의미한다. 데이터 분석은 JASP 0.18.2.0(University of Amsterdam)을 사용하 여 일원분산분석 Levene's 검정을 실시 하였고, F=2.112, p=0.099 > α=0.05 등분산으로 유의미하게 분석 되었고, 분산분석표(Analysis of Variance Table)로 F값 1.429, p=0.250 > α=0.05 으로 ‘3m 거리의 RL-GR의 양안 시력 1.0 이상의 남자 6명의 인지능력의 평균 300 ms 는 동일하다’ 라는 귀무가설(H0)은 채택 되었다. 또한 튜키 사후검정(Tukey HSD)을 통하여, 신뢰구간 안에 0을 포함하여 ‘그룹 간 평균차이가 없다’ 는 귀무가설(H0)을 채택 되었다. 본 연구는 RL-GR 반사광이 암순응 상태에서 시각적 인지 능력에 긍정적인 영향을 미친다는 것을 확인하였고, 사고예방을 위한 반사광 활용의 시사점을 제시하였다.

The purpose of this study is to experimentally analyze the seismic performance of a vertical irregular beam-column specimen reinforced with RBS (Replaceable Steel Brace System), a steel brace system. To evaluate the seismic performance of RBS, three specimens were manufactured and subjected to cycle loading tests. The stiffness ratio of beam-upper column of the non-retrofitted specimen was 1.2, and those of the two retrofitted specimens were 1.2 and 0.84. The stiffness ratio of the beam-lower column of all specimens was 0.36. And the stiffness ratio were used for variable. As a result of the experiment, the specimen retrofitted with RBS showed improved maximum load, effective stiffness and energy dissipation capacity compared to the non-retrofitted specimen with the same beam-upper column stiffness ratio. The specimen with 0.84 beam-upper column stiffness ratio showed improved performance compared to the specimen with 1.2 stiffness ratio.

In this research, the concrete breakout strength in tension of cast-in-place anchors (CIP) is experimentally investigated to be used as fundamental data for the seismic fragility analysis of equipment in nuclear power plants. Experimental variables are chosen, such as the embedment depth of the anchor, single/group anchor configurations, diameter of the head plate, and crack width. Monotonic and cyclic loading are applied to all types of specimens. As measured from the experiments, concrete breakout strength in tension is 1.5 to 2 times higher than the expected strengths from concrete capacity design (CCD) method-based model equations. In alignment with the model’s predictions, concrete breakout strength increases with deeper embedment depth, and the strength of group anchors also increases based on the expansion of the projected concrete failure area. This study also explores the effects of head plate diameter and crack width, which are not considered in the model equation. Experimental results show that the diameter of the head plate is not directly correlated to the concrete breakout strength, whereas the crack width is. The presence of cracks, with widths of 0.3 mm and 0.5 mm, leads to reductions of approximately 7% and 17%, respectively, compared to single anchors in non-cracked concrete.

In this study, the calorimeter was used to experimentally investigate the heating characteristics of the variable A/C system according to changes in loading time and outdoor dry bulb temperature. The heating capacity, COP and compressor discharge temperature were measured while changing the loading time of the compressor. To develop the correlation for compressor discharge temperature, loading time, indoor dry bulb temperature and outdoor dry bulb temperatures were considered as operating variables. As the outdoor temperature and loading time increased, the heating capacity and COP increased. However, the change in COP showed different trends depending on the outdoor temperature. The evaporation temperature according to the loading time is a good estimate of the outdoor temperature. However, as the temperature difference between indoor and outdoor rooms decreases and the loading time increases, the condensation pressure increases significantly, so the condensation temperature increases. The maximum deviation between the correlation and the experimental value for compressor discharge temperature was within approximately 2℃.

This study investigates the thermal expansion characteristics of hydroxyl-terminated polybutadiene(HTPB) based solid propellants, focusing on batch-to-batch variability and accelerated aging effects. Coefficient of thermal expansion(CTE) measurements were conducted using thermomechanical analyzer(TMA) on samples from different manufacturing batches and specimens aged at various temperatures for different durations. Results indicate variations in CTE values between batches, highlighting the significance of manufacturing process control. Accelerated aging experiments reveal minimal systematic changes in CTE, suggesting stability of thermal expansion properties under short-term thermal stress. The overall distribution of CTE values shows concentration within a specific range, indicating consistency in thermal expansion characteristics. These findings provide insights into the thermal behavior of HTPB-based solid propellants, contributing to improved missile design and lifecycle prediction models.

In this study, the calorimeter was used to experimentally investigate the cooling characteristics of the variable A/C system according to changes in loading time and outdoor dry bulb temperature. The cooling capacity, COP and compressor discharge temperature were measured while changing the loading time of the compressor. To develop the correlation for compressor discharge temperature, loading time, indoor and outdoor dry bulb temperatures, evaporation and condensation temperatures were considered as operating variables. As the loading time increased, the cooling capacity and COP increased. The cooling capacity increased linearly with the loading time. The COP increased more at low loading times than at high loading times. The change in condensing temperature according to the loading time had a small temperature fluctuation range, and the evaporation temperature decreased linearly. The compressor discharge temperature increased linearly with the loading time and outdoor temperature, and the maximum deviation between the experimental value and the correlation was within about 2℃.