• 대한기계학회논문집A
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• 제29권6호
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• pp.822-827
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• 2005

The characteristics of elastic waves emanating from crack initiation and propagation in 6061 aluminum alloy subjected to fatigue loading with different stress ratio was investigated. The objective of this study is to determine the properties of the signals generated from each stage of fatigue crack growth. AS a crack propagates, substantial elastic wave occurred just prior to penetration. Then it decreased and the crack penetrated. The waveforms and their power spectra were found to be dependent on the different stress ratio associated with the signals. It is determined that high-frequency signal $0.5{\sim}0.75$ MHz is most likely emitted during crack propagation at peak load of fatigue cycle which release the highest energy. It is determined that 0.3 MHz is closely related to crack closure effect. The frequency peaks below 0.25 MHz may be attributed to fretting or hydraulic noise.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.487-492
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• 2007

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchical void element with the integrals of Legend polynomials is used to characterize the fracture behavior of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. The numerical approach is based on the v-version degenerate shell element including the theory of anisotropic laminated composites. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness of materials. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of hierarchical void element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem.

• 대한한방부인과학회지
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• 제18권3호
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• pp.51-66
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• 2005

Purpose : Investigate the effects of Haeganjeon water extract (HGJ) on immobilization-stress or cold-stress in C57BL/6J mice. Methods : Male C57BL/6J 30 mice of weighting 18${\pm}$2g, were divided into sixs groups including the immobilization-stress group(5heads), after immobilization-stress HGJ oral administration(500mg/kg) groups(5heads), cold-stress group(5heads) and after cold-stress HGJ oral administration(500mg/kg) groups(5heads). then we observed changes in the serum histamine and corticosterone level and changes immune system. Results : HGJ decreased the serum level of histamine and corticosterone increased by immobilization-stress or cold-stress. HGJ inhibited the release of histamine from mast cells. In addition, HGJ enhanced the cell viability of thymocytes decreased by immobilization-stress or cold-stress and decreased DNA fragmentation of thymocytes increased by immobilization- stress or cold-stress. Also, HGJ increased the cell viability of splenocytes decreased by cold-stress and decreased DNA fragmentation of splenocytes increased by cold-stress. HGJ decreased the population of thymic CD4+ cells increased by immobolization-stress. HGJ increased the population of B220+ cells decreased by immobilization-stress and decreased the population of Thy1+ cells increased by immobilization-stress. Also, HGJ decreased the population of splenic CD4+ cells increased by immobolization-stress. HGJ enhanced the production of ${\gamma}-interferon$ decreased by immobilization-stress or cold-stress and increased the production of interleukin-4 decreased by immobilization-stress. Furthermore, HGJ enhanced the phagocytic activity decreased by immobilization-stress or cold-stress and enhanced the level of nitric oxide decreased by immobilization-stress or cold-stress. Conclusion : HGJ may be useful for the prevention and treatment of stress via suppression of serum histamine and corticosterone level and enhancement of immune response.

• Corrosion Science and Technology
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• 제11권6호
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• pp.275-279
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• 2012

Ni-W alloy deposits have lately attracted the interest as an alternative surface treatment method for hard chromium electrodeposits because of higher wear resistance, hardness at high temperature, and corrosion resistance. This study deals with influences of process variables, such as electodeposition current density, plating temperature and pH, on the internal stress of Ni-W nanocrystalline deposits. The internal stress was increased with increasing the applied current density. With increasing applied current density, the grain size of the deposit decreases and concentration of hydrogen in the deposit increases. The subsequent release of the hydrogen results in shrinkage of the deposit and the introduction of tensile stress in the deposit. Consequently, for layers deposited at high current density, cracking occurs readily owing to high tensile stress value. By increasing the temperature of the electrodeposition from $60^{\circ}C$ to $80^{\circ}C$, the internal stress was decreased. It seems that an increase in the number of active ions overcoming the activation energy at elevated temperature caused a decline in the concentration polarization and surface diffusion. It decreased the level of hydrogen absorption due to the lessened hydrogen evolution reaction. Therefore, the lower level of hydrogen absorption degenerated the hydride on the surface of the electrode, resulting in the reduction of the internal stress of the deposits. By increasing the pH of the electrodeposition from 5.6 to 6.8, the internal stress in the deposits were slightly decreased. It is considered that the decrease in internal stess of deposits was due to supply of W complex compound in cathode surface, and hydrogen ion resulted from decrease of activity.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2001년도 춘계학술대회
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• pp.311-317
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• 2001

The notched Charpy and Izod impact tests are the most prevalent techniques used to characterize the effects of high impulse loads on ploymeric materials. An analysis method for rubber toughened PVC is suggested to evaluate critical strain energy release rates(Gc) from the Charpy impact energy measurements. An Instrumented Charpy Impact tester was used to extract ancillary information concerning fracture properties in addition to total fracture properties and maximum critical loads. The stress intensity factor Kd was computed for varying amounts of rubber contents from the obtained maximum critical loads and also toughening effects were investigated as well.

• 대한토목학회논문집
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• 제32권1A호
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• pp.11-18
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• 2012

이 논문에서는 유리-에폭시 섬유 보강 복합재료판에 $K_I$ 과 $K_{II}$ 에 의한 혼합모우드 상태의 균열된 알루미늄판의 응력확대계수의 수치해석 산정을 다루고 있다. 응력확대계수 산정을 위한 가상균열닫힘법과 2단계 확장법이 고려된다. 에너지 방출률과 응력확대계수의 항으로 표현되는 파괴역학 매개변수 계산을 위하여, p-수렴 부분 층별모델이 채택된다. 고려되는 p-수렴 방식은 저매개변수 요소의 개념에 기초한다. 1개 층에 대해 가정된 변위장, 변위-변형률 관계, 그리고 3차원 구성방정식은 2차원과 1차원 고차 형상함수의 조합으로 정의된다. 고려되는 요소는 변위장의 보간과 수치적분을 수행하기 위해 로바토 형상함수와 가우스-로바토 적분법이 사용된다. 언급된 모델과 기법들을 사용하여, 경사각도의 변화에 따른 적층판 형상의 효과와 접착제의 강도가 팻치보강 시스템에 미치는 영향이 조사된다. 중립축 변화에 따른 팻치보강 적층판의 면외 휨 효과도 분석된다. 고려되는 모델의 정확성과 단순성 등에 관해서 응력확대계수, 응력분포, 자유도 수, 에너지 방출률 등의 항목을 가지고서 평가된다.

• 한국식품영양과학회지
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• 제46권2호
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• pp.161-168
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• 2017

본 연구에서는 산화적 스트레스로 유도한 시신경 세포사멸에 대한 차조기 물 추출물(PFE)의 효과를 확인하였다. Staurosporine으로 분화된 ssdRGC-5 세포에 buthionine과 glutamate(B/G)로 산화적 스트레스를 유도하였으며, LDH release assay, MTT reduction assay를 통하여 PFE가 농도 의존적으로 B/G에 의한 세포사멸을 억제함을 관찰하였다. 세포사멸의 기전을 연구하기 위해 caspase 활성, 세포 내 ROS 생성량, 세포고사 관련 단백질 발현을 관찰한 결과, B/G에 의해 증가한 ROS 생성량, caspase 활성을 PFE가 억제하였고, 세포질로 방출된 cytochrome c와 미토콘드리아로 이동한 Bax도 감소함을 확인하였다. 이상의 결과로부터 차조기는 산화적 스트레스로 유도된 시신경 세포사멸 과정에서 항산화 효과와 미토콘드리아성 세포사멸을 완화함으로써 세포 보호 작용을 나타냄을 확인하였다.

• Molecules and Cells
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• 제43권10호
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• pp.848-855
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• 2020

Cells assemble stress granules (SGs) to protect their RNAs from exposure to harmful chemical reactions induced by environmental stress. These SGs release RNAs, which resume translation once the stress is relieved. During stem cell differentiation, gene expression is altered to allow cells to adopt various functional and morphological features necessary to differentiate. This process induces stress within a cell, and cells that cannot overcome this stress die. Here, we investigated the role of SGs in the progression of stem cell differentiation. SGs aggregated during the neuronal differentiation of human bone marrow-mesenchymal stem cells, and not in cell lines that could not undergo differentiation. SGs were observed between one and three hours post-induction; RNA translation was restrained at the same time. Immediately after disassembly of SGs, the expression of the neuronal marker neurofilament-M (NF-M) gradually increased. Assembled SGs that persisted in cells were exposed to salubrinal, which inhibited the dephosphorylation of eukaryotic translation initiation factor 2 subunit 1 (eIF2α), and in eIF2α/S51D mutant cells. When eIF2α/S51A mutant cells differentiated, SGs were not assembled. In all experiments, the disruption of SGs was accompanied by delayed NF-M expression and the number of neuronally differentiated cells was decreased. Decreased differentiation was accompanied by decreased cell viability, indicating the necessity of SGs for preventing cell death during neuronal differentiation. Collectively, these results demonstrate the essential role of SGs during the neuronal differentiation of stem cells.

• Food Science and Biotechnology
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• 제16권6호
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• pp.1035-1040
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• 2007

Epidemiologic studies have shown important relationships between oxidative stress and Alzheimer's disease (AD) brain. In this study, free radical scavenging activity and neuronal cell protection effect of aqueous methanol extracts of Acanthopanax senticosus (A. senticosus) were examined. $H_2O_2$-induced oxidative stress was measured using 2',7'-dichlorofluorescein diacetate (DCF-DA) assay. Pretreatment with the phenolics of A. senticosus prevented oxidative injury against $H_2O_2$ toxicity. Since oxidative stress is known to increase neuronal cell membrane breakdown, leading to cell death, lactic dehydrogenase release, and trypan blue exclusion assays were utilized. We found that phenolics of A. senticosus have neuronal cell protection effects. It suggests that the phenolics of A. senticosus inhibited $H_2O_2$-induced oxidative stress and A. senticosus may be beneficial against the oxidative stress-induced risk in AD.

• 대한불안의학회지
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• 제13권1호
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• pp.39-45
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• 2017

Objective : Korean employees tend to release their stress by alcohol drinking. This study aimed to investigate the association between job stress and problematic drinking in Korean employees. Methods : The study participants were 72,119 employees who attended health screenings and responded to the Alcohol Use Disorder Identification Test-Korea (AUDIT-K), Korean Occupational Stress Scale-Short Form (KOSS-SF), Center for Epidemiologic Study-Depression (CES-D), Beck Anxiety Inventory (BAI) and questionnaire on suicidal ideation and sociodemographic characteristics. We investigated the sociodemographic and clinical characteristics of the problematic drinking group ($AUIDT-K{\geq}12$) and used binary logistic regression to determine the impact of job stress on problematic drinking. Results : Age, gender, marital status, education year, sleep duration, obesity, smoking, suicidal ideation, and depression and anxiety showed significant differences between the problematic drinking group and normal group. Among the various kinds of job stresses, job insecurity and lack of reward were associated with problematic drinking. Conclusion : The result of this study suggested that certain kinds of job stress might be associated with problematic drinking in Korean employees.