• Asian Pacific Journal of Cancer Prevention
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• 제17권2호
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• pp.829-833
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• 2016

Purpose: To investigate the work associated stress and nicotine dependence among law enforcement personnel in Mangalore, India. Materials and Methods: A cross-sectional questionnaire survey was conducted among law enforcement personnel in Mangalore, India. Demographic details, stress factors experienced at work and nicotine dependency were the variables studied. The extent of stress factors experienced at work was assessed using the Effort-Reward Imbalance scale (ERI). Nicotine dependence was measured using the Fagerstrom Test for Nicotine Dependence (FTND) and the Fagerstrom Test for Nicotine Dependence-Smokeless Tobacco (FTND-ST). Logistic regression was used for the statistical analysis. Results: Three hundred and four law enforcement personnel participated in the study, among whom 68 had the presence of one or more habits like tobacco smoking, tobacco chewing and alcohol use. The mean effort score was $15.8{\pm}4.10$ and the mean reward and mean overcommitment scores were $36.4{\pm}7.09$ and $17.8{\pm}5.32$ respectively. Effort/Reward ratio for the total participants was 1.0073 and for those with nicotine habit was 1.0850. Results of our study demonstrated no significant association between domains of ERI scale and presence of habits but work associated stress was associated with the presence of one or more habits. Compared to constables, head constables had 1.12 times higher risk of having a nicotine habit. Conclusions: Our study implies job designation is associated with nicotine habits. However, there was no association between work associated stress and nicotine dependence among law enforcement personnel in Mangalore.

• 대한기계학회논문집A
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• 제27권1호
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• pp.200-207
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• 2003

In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities of shot balls on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are being commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage II and the threshold stress intensity factor range Δ$K_{th}$ in stage I. Also the material constant C and the crack propagation index m in the formula of paris law da/dN= C $({\Delta}K^m)$ were suggested in this work to estimate the dependency on the shot velocity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1315-1320
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• 2003

The thermal expansion coefficient, which causes the micro failure at the interfacial state of thin films is necessary to consider for proper designing MEMS. The effect of temperature on the coefficient of thermal expansion(CTE) of $SiO_2$ and $Si_3N_4$ film was investigated. Thermal strain induced by mismatch of CTE between substrate and thin film continuously measured with resolution-improved electronic speckle pattern interferometry(ESPI). The thermal stress induced by mismatch of CTE derivate through thermal strain. The thermal expansion coefficients of thin film were calculated with the general equation of CTE and thermal stress in thin films, and it confirmed that CTE of $SiO_2$changed from $0.25{\times}10^{-6}/^{\circ}C$ to $1.4{\times}10^{-6}/^{\circ}C$ with temperature increasing from 50 to $600^{\circ}C$

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.492-497
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• 2005

In this study, we propose an advanced nanoindentaion test, Nano Pillar Compression Test (NPCT) to measure a stress-strain relation for micro scale polymer structures. Firstly, FEM analysis is performed to research behavior of micro polymer pillars in several specimen aspect ratios and different friction conditions between specimen and tip. Based on the FEM results, micro scale UV-curable polymer pillars are fabricated on a substrate by Nano Stereo Lithography (NSL). To measure their mechanical properties, uniaxial compression test is performed using nanoindentation apparatus with flat-ended diamond tip. In addition, the dependency of compression properties on loading condition and specimen size are discussed.

• Wind and Structures
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• 제32권1호
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• pp.31-46
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• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Steel and Composite Structures
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• 제47권3호
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• pp.355-363
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• 2023

The main purpose of this study is to characterize the size-dependent strain rate sensitivity in structural steel using the continue stiffness measurement (CSM) indentation. A series of experiments, such as CSM indentation and optical microscope examination, has been performed at the room temperature at different rate conditions. The results indicated that indentation hardness, strain rate, and flow stress showed size-dependent behavior. The dependency of indentation hardness, strain rate, and flow stress on the indentation size was attributed to the transition of the dislocation nucleation rate and the dislocation behaviors during the indentation process. Since both hardness and strain rate showed the size-dependent behavior, SRS tended to depend on the indentation depth. The results indicated that the SRS was quite high over 2.0 at the indentation depth of 240 nm and quickly dropping to 0.08, finally around 0.046 at large indents. The SRS values at large indentations strongly agree with the general range reported for several types of low-carbon steel in the literature (Chatfield and Rote 1974, Nguyen et al. 2018b, Luecke et al. 2005). The results from the present study can be used in both static and dynamic analyses of structures as well as to assess and understand the deformation mechanism and the stress-state of material underneath the indenter tip during the process of the indentation testing.

• 대한기계학회논문집
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• 제11권6호
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• pp.953-962
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• 1987

본 연구에서는 국산 구조용강의 SM 45C 와 SUS 304 재를 최고 강도치가 나타 나는 압접조건하에서 압접하여 우재료의 용착금속부, 열영향부, 각 모재부 소정의 장 소에 미소원공을 가공한 시험편을 토대로 피로크랙의 발생 및 전파거동을 응력 레벨의 고저를 고려하여 고찰하였다.

• 비파괴검사학회지
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• 제26권5호
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• pp.285-290
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• 2006

고장력볼트의 체결상태를 평가하는 것은 체결볼트의 안전유지관리 측면에서 매우 중요하다. 본 논문에서는 초음파의 음속이 응력에 의존하는 이른바 음탄성효과에 기초하여 초음파의 전파시간(TOF)를 측정함으로써 볼트에 작용하는 축응력을 평가하는 방법을 제안한다. 그런데 일반적으로 볼트체결시 볼트에 작용하는 응력범위내에서의 음속 변화량은 매우 작으며, 따라서 TOF 측정에 있어서 높은 정밀도가 요구된다. 이를 위해 본 논문에서는 톤버스트파형의 초음파를 이용한 위상검출법을 적용하였다. 제안된 원리는 실험을 통해 검증되었으며, 볼트 축응력 측정의 유효성을 검증하기 위해 스트레인게이지를 이용한 축응력 측정결과와 비교하였다. 두 결과는 양호한 일치를 보였으며, 이로써 제안한 방법이 체결된 고장력볼트의 체결상태 평가에 유용하다는 결론을 얻을 수 있었다.

• Journal of Microbiology and Biotechnology
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• 제17권9호
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• pp.1452-1459
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• 2007

The Dps protein, which is overexpressed in harsh environments, is known to playa critical role in the protection of DNA against oxidative stresses. In this study, the roles of Fur in the expression of the dps gene in Salmonella and the protection mechanisms against oxidative stress in Salmonella cells preexposed to iron-stress were investigated. Two putative Fur boxes were predicted within the promoter region of the S. typhimurium dps gene. The profile of dps expression performed by the LacZ reporter assay revealed growth-phase dependency regardless of iron-status under the culture conditions. The fur mutant, $_X4659$, evidenced a reduced level of ${\beta}$-galactosidase as compared to the wild-type strain. The results observed after the measurement of the Dps protein in various Salmonella regulatory mutants were consistent with the results acquired in the reporter assay. This evidence suggested that Fur performs a function as a subsidiary regulator in the expression of dps. The survival ability of Salmonella strains after exposure to oxidative stress demonstrated that the Dps protein performs a pivotal function in the survival of stationary-phase S. typhimurium against oxidative stress. Salmonella cells grown in iron-restricted condition required Dps for full protection against oxidative stress. The CK24 (${\Delta}dps$) cells grown in iron-replete condition survived at a rate similar to that observed in the wild-type strain, thereby suggesting the induction of an unknown protection mechanism(s) other than Dps in this condition.

• 한국지반공학회논문집
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• 제24권4호
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• pp.37-46
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• 2008

포장재료의 역학적 특성을 대표하는 회복탄성계수는 '86 AASHTO 설계법에서 노상의 기본입력 물성치로 적용한 이후 포장 설계, 해석뿐 아니라 포장 평가, 유지관리 등에도 보편적 개념으로 정착되어 가고 있다. 국내 노상토의 회복탄성계수는 함수비와 건조단위중량으로 대표되는 재료적 요인과 축차응력 및 구속응력에 대단히 큰 영향을 받고 있고, 하중주파수의 영향은 있으나 그 정도가 크지 않고, 하중반복횟수의 영향은 무시 가능한 것으로 알려져 있다(건설교통부 2003). 따라서 국내 포장재료에 따른 회복탄성계수의 적절한 평가는 국내 포장구조체의 역학거동 및 공용성 평가를 위해 매우 중요한 사항이다. 이와 같은 배경으로 본 연구에서는 국내 노상토 재료의 역학적 특성 변화를 포장 단면설계에 합리적으로 반영하기 위한 노상토 해석모델을 제안하였고, 제안된 모델을 적용한 유한요소해석 결과와 시험도로 실측치와의 비교 검증을 통해 제안된 모델의 신뢰성을 검증하였다.