• 한국지진공학회논문집
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• 제3권3호
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• pp.21-32
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• 1999

지진가속도에 의한 부재의 지진거동 특성은 실험적인 방법 또는 등가의 정적실험으로부터 추정되어 온 것이 대부분이다 본 연구에서는 지진가속도에 의한 철근콘크리트 전단벽체의 지진응답 및 파괴거동 특성을 유한요소법을 사용한 해석적인 기법에 의해서 예측하였다 콘크리트 부재에서 균열은 필연적으로 발생하게 되며 이로 인한 부재의 강도 및 강성의 감소 철근의 항복 및 하중의 반복성으로 인한 균열의 개폐등이 수반된다 본 연구에서는 이와 같은 콘크리트와 철근의 비선형 특성을 고려한 이축응력상태에 대한 재료모델과 동적해석 알고리즘을 범용 수치해석기법인 유한요소법을 사용하여 해석프로그램으로 구현하였다 지진가속도를 받는 전단벽을 대상으로 지진응답 및 파괴거동등을 본 연구의 해석적인 방법으로 예측하였으며 그 결과를 신뢰성 있는 연구자의 실험결과와 비교하여 그 타당성을 검증하였다.

• Animal Bioscience
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• 제34권11호
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• pp.1839-1848
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• 2021

Objective: The objective of the present study was to investigate the comparative effects of dietary functional nutrients including glutamine (Gln), chromium picolinate (Cr picolinate), vitamin C (Vit C), betaine (Bet), and taurine (Tau) on growth performance, meat quality, immune responses, and stress biomarkers in broiler chickens raised under heat stress conditions. Methods: A total of 420 21-d-old Ross 308 male broiler chickens (initial body weight = 866±61.9 g) were randomly allotted to 1 of 7 treatment groups with 6 replicates. One group was kept under thermoneutral conditions and was fed a basal diet (PC, positive control). Other 6 groups were exposed to a cyclic heat stress condition. One of the 6 groups was fed the basal diet (NC, negative control), whereas 5 other groups were fed the basal diet supplemented with 0.5% Gln, 500 ppb Cr picolinate, 250 mg/kg Vit C, 0.2% Bet, or 1.0% Tau. The diets and water were provided ad libitum for 21 d. Results: Broiler chickens in NC group had decreased (p<0.05) growth performance and immune responses measured based on cutaneous basophil hypersensitivity (CBH), but increased (p<0.05) stress responses measured based on feather corticosterone concentrations and blood heterophil:lymphocyte than those in PC group. However, none of dietary functional nutrients had a positive effect on growth performance of broiler chickens. Dietary supplementation of 250 mg/kg Vit C improved (p<0.05) CBH responses of broiler chickens, but other functional nutrients had no such an improvement in CBH responses. All functional nutrients decreased (p<0.05) stress responses of broiler chickens. Conclusion: Functional nutrients including Gln, Cr picolinate, Vit C, Bet, and Tau at the supplemental levels used in this study decrease stress responses of broiler chickens to a relatively similar extent. However, this reduction in stress responses could not fully ameliorate decreased productive performance of broiler chickens raised under the current heat stress conditions.

• 한국지반환경공학회 논문집
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• 제23권5호
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• pp.5-13
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• 2022

본 연구에서는 국내 지진모의시험 수행 시 모래지반의 모사를 위해 국내에서 널리 이용되는 지반재료인 인공규사를 대상으로 상대밀도 차이에 따른 진동삼축시험을 수행하여 인공규사의 동적특성 및 액상화 저항특성을 실험적으로 분석하였다. 상대밀도 조건을 40%, 60%, 80%로 달리한 시험결과를 통해 상대밀도에 따른 액상화 저항특성을 확인하였으며, 액상화 진동저항응력비(Cyclic resistance stress ratio, CRR) 산정 곡선을 도시하였다. 또한, 액상화 진동저항응력비(CRR) 산정곡선의 타당성을 검토하기 위해 실내진동삼축시험에 사용된 규사로 이루어진 인공지반을 조성한 후, 간편예측법과 상세예측법을 통한 액상화 평가를 수행하여 각각의 안전율을 비교·검토하였다. 최종적으로, 상대밀도를 달리한 실험을 통해 인공규사의 동적물성을 파악하여 결과를 도출하였으며, 이 결과를 물성치로 적용한 상대밀도 40% 간편예측법은 안전율이 1로 안전한 지반으로 도출된 반면 상세예측법은 0.05작은 값으로 결과가 도출되었다.

• 대한토목학회논문집
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• 제43권4호
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• pp.469-476
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• 2023

반복하중이나 동적하중에 대한 지반의 소성모델은 지반구조물의 비선형 수치해석에 매우 중요하다. 단일 항복면 모델은 반복하중에 대해 선형적 거동을 보이는 반면, 개발된 탄성영역이 없는 J₂-경계면 소성모델은 동일한 물성치로 효과적으로 지반의 비선형성을 모사할 수 있다. 경계면 내부 항복면의 반경을 0으로 수렴시켜 탄성영역이 사라지도록 수식화하고, 소성경화 계수과 팽창률을 이용하여 소성변형 증분을 정의하였다. 개발된 모델의 응력-변형률 증분식을 제시하고, 쌍곡선 모델에 대한 소성경화 계수를 유도하였다. 삼축압축조건과 얕은기초의 반복하중에 대한 비교해석은 개발된 모델의 안정적인 수렴성, 이론식과의 일치성, 그리고 이력경로을 보여 주었다. 또한, 수정된 쌍곡선함수에 대한 소성경화 계수를 제시하여, 1차원 등가선형모델에 부합하는 모델변수 산정법을 제안하여 지반의 다차원 거동을 모델링할 수 있도록 하였다.

• Journal of Microbiology and Biotechnology
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• 제21권11호
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• pp.1184-1192
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• 2011

A bacterial isolate (strain JS-2) characterized as Bacillus sp. was challenged with high concentrations of toxic selenite ions. The microbe was found to transform the toxic, soluble, colorless selenite (${SeO_3}^{2-}$) oxyions to nontoxic, insoluble, red elemental selenium ($Se^0$). This process of biotransformation was accompanied by cytoplasmic and surface accumulation of electron dense selenium ($Se^0$) granules, as revealed in electron micrographs. The cells grown in the presence of selenite oxyions secreted large quantities of extracellular polymeric substances (EPS). There were quantitative and qualitative differences in the cell wall fatty acids of the culture grown in the presence of selenite ions. The relative percentage of total saturated fatty acid and cyclic fatty acid increased significantly, whereas the amount of total unsaturated fatty acids decreased when the cells were exposed to selenite stress. All these physiological adaptive responses evidently indicate a potentially important role of cell wall fatty acids and extracellular polymeric substances in determining bacterial adaptation towards selenite-induced toxicity, which thereby explains the remarkable competitiveness and ability of this microbe to survive the environmental stress.

• Mycobiology
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• 제38권1호
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• pp.26-32
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• 2010

The cyclic AMP (cAMP) pathway plays a major role in growth, sexual differentiation, and virulence factor synthesis of pathogenic fungi. In Cryptococcus neoformans, perturbation of the cAMP pathway, such as a deletion in the gene encoding adenylyl cyclase (CAC1), causes defects in the production of virulence factors, including capsule and melanin production, as well as mating. Previously, we performed a comparative transcriptome analysis of the Ras- and cAMP- pathway mutants, which revealed 163 potential cAMP-regulated genes (38 genes at a 2-fold cutoff). The present study characterized the role of one of the cAMP pathway-dependent genes (serotype A identification number CNAG_ 06576.2). The expression patterns were confirmed by Northern blot analysis and the gene was designated cAMP-regulated gene 1 (CAR1). Interestingly, deletion of CAR1 did not affect biosynthesis of any virulence factors and the mating process, unlike the cAMP-signaling deficient cac1$\Delta$ mutant. Furthermore, the car1$\Delta$ mutant exhibited wild-type levels of the stress-response phenotype against diverse environmental cues, indicating that Car1, albeit regulated by the cAMP-pathway, is not essential to confer a cAMP-dependent phenotype in C. neoformans.

• 대한기계학회논문집A
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• 제26권3호
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• pp.537-543
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• 2002

This paper examines a new in-process measurement system for the measurement of micro-defects on the surfaces of brittle materials by using the AFM (Atomic Force Microscopy). A new AFM scanning stage that can also perform nano-scale bending of the sample was developed by adding a bending unit to a commercially available AFM scanner. The bending unit consists of a PZT actuator and sample holder, and can perform static and cyclic three-point bending. The true bending displacement of the bending unit is approximately 1.8mm when 80 volts are applied to the PZT actuator. The frequency response of the bending unit and the stress on the sample were also analyzed, both theoretically and experimentally. Potential surface defects of the sample were successfully detected by this measurement system. It was confirmed that the number of micro-defects on a scratched surface increases when the surface is subjected to a cyclic bending load.

• 동력기계공학회지
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• 제18권5호
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• pp.115-121
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• 2014

Alloy 617 is the one of the leading candidate materials for intermediate heat exchangers(IHX) of a very high temperature reactor(VHTR) system. Some of the components are joined by many welding techniques and therefore the welded joints are inevitable in the construction of systems. In the present paper, the low cycle fatigue(LCF) behaviors of Alloy 617 base metal(BM) and the gas tungsten arc welded (GTAWed) weld joints(WJ) are investigated experimentally under strain controlled LCF tests. Fully axial total-strain controlled tests have been conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. The weld joints have shown a lower fatigue lives compared with base metals at all the testing conditions. The weld joints have shown a higher cyclic stress response behavior than base metal. Both BM and WJ exhibited cyclic strain hardening behavior, depending on the total strain range. In addition, the strain-life parameters for BM and WJ were determined, based on Coffin-Manson equations.

• Computers and Concrete
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• 제25권4호
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• pp.293-302
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• 2020

Connections play a significant role in strength of structures against earthquake-induced loads. According to the post-seismic reports, connection failure is a cause of overall failure in reinforced concrete (RC) structures. Connection failure results in a sudden increase in inter-story drift, followed by early and progressive failure across the entire structure. This article investigated the cyclic performance and behavioral improvement of shape-memory alloy-based connections (SMA-based connections). The novelty of the present work is focused on the effect of shape memory alloy bars is damage reduction, strain recoverability, and cracking distribution of the stated material in RC moment frames under seismic loads using 3D nonlinear static analyses. The present numerical study was verified using two experimental connections. Then, the performance of connections was studied using 14 models with different reinforcement details on a scale of 3:4. The response parameters under study included moment-rotation, secant stiffness, energy dissipation, strain of bar, and moment-curvature of the connection. The connections were simulated using LS-DYNA environment. The models with longitudinal SMA-based bars, as the main bars, could eliminate residual plastic rotations and thus reduce the demand for post-earthquake structural repairs. The flag-shaped stress-strain curve of SMA-based materials resulted in a very slight residual drift in such connections.

• Molecules and Cells
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• 제45권5호
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• pp.306-316
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• 2022

Chronic stress contributes to the risk of developing depression; the habenula, a nucleus in epithalamus, is associated with many neuropsychiatric disorders. Using genome-wide gene expression analysis, we analyzed the transcriptome of the habenula in rats exposed to chronic restraint stress for 14 days. We identified 379 differentially expressed genes (DEGs) that were affected by chronic stress. These genes were enriched in neuroactive ligand-receptor interaction, the cAMP (cyclic adenosine monophosphate) signaling pathway, circadian entrainment, and synaptic signaling from the Kyoto Encyclopedia of Genes and Genomes pathway analysis and responded to corticosteroids, positive regulation of lipid transport, anterograde trans-synaptic signaling, and chemical synapse transmission from the Gene Ontology analysis. Based on protein-protein interaction network analysis of the DEGs, we identified neuroactive ligand-receptor interactions, circadian entrainment, and cholinergic synapse-related subclusters. Additionally, cell type and habenular regional expression of DEGs, evaluated using a recently published single-cell RNA sequencing study (GSE137478), strongly suggest that DEGs related to neuroactive ligand-receptor interaction and trans-synaptic signaling are highly enriched in medial habenular neurons. Taken together, our findings provide a valuable set of molecular targets that may play important roles in mediating the habenular response to stress and the onset of chronic stress-induced depressive behaviors.