• Coupled systems mechanics
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• 제8권6호
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• pp.501-522
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• 2019

The present study is concerned with the thermoelastic interactions in a two dimensional axisymmetric problem in transversely isotropic thermoelastic solid using new modified couple stress theory without energy dissipation and with two temperatures. The Laplace and Hankel transforms have been employed to find the general solution to the field equations. Concentrated normal force, normal force over the circular region, concentrated thermal source and thermal source over the circular region have been taken to illustrate the application of the approach. The components of displacements, stress, couple stress and conductive temperature distribution are obtained in the transformed domain. The resulting quantities are obtained in the physical domain by using numerical inversion technique. The effect of two temperature varying by taking different values for the two temperature on the components of normal stress, tangential stress, conductive temperature and couple stress are depicted graphically.

• Molecules and Cells
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• 제26권6호
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• pp.616-620
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• 2008

Maintaining redox balance is one of the crucial requirements for a cell to endure stress from the outside. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) plays an important role in the ascorbate-glutathione cycle; one of the major ROS scavenging systems in most known biological systems. A cDNA clone of the DHAR gene from Oryza sativa (OsDHAR) was isolated and overexpressed in Escherichia coli BL21 (DE3) strain from the pET-28a(+) expression vector. The OsDHAR transformed E. coli cells showed significantly higher DHAR activity and a lower level of ROS than the E. coli cells transformed by an empty pET-28a(+) vector. Also, the DHAR-overexpressing E. coli strain was more tolerant to oxidant- and heavy metal-mediated stress conditions than the control E. coli strain. The results suggest that the overexpressed rice DHAR gene effectively functions in a prokaryotic system and provide protection to various oxidative stresses.

• Journal of the Korean Statistical Society
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• 제28권4호
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• pp.415-433
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• 1999

This paper considers the design of step-stress accelerated life tests for the Weibull distribution with a nonconstant shape parameter under Type I censoring. It is assumed that scale and shape parameters are log-linear functions of (possibly transformed) stress and that a cumulative exposure model holds for the effect of changing stress. The asymptotic variance of the maximum likelihood estimator of a stated quantile at design stress is used as an optimality criterion. The optimum three step-stress plans are presented for selected values of design parameters and the effects of errors in pre- estimates of the design parameters are investigated.

• Journal of the Korean Data and Information Science Society
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• 제21권4호
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• pp.813-818
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• 2010

The least squares estimation method for model parameters under failure step-stress accelerated life tests is studied and a numerical example will be given to illustrate the proposed inferential procedures under the compound linear plans proposed as an alternative to the optimal quadratic plan, assuming that the exponential distribution with a quadratic relationship between stress and log-mean lifetime. The proposed compound linear plan for constant stress accelerated life tests and 4:2:1 plan are compared for various situations. Even though the compound linear plan was proposed under constant stress accelerated life tests, we found that this plan did well relatively in failure step-stress accelerated life tests.

• Structural Engineering and Mechanics
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• 제76권1호
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• pp.17-26
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• 2020

The objective of this paper is to study the deformation in transversely isotropic thermoelastic solid using new modified couple stress theory subjected to ramp-type thermal source and without energy dissipation. This theory contains three material length scale parameters which can determine the size effects. The couple stress constitutive relationships are introduced for transversely isotropic thermoelastic solid, in which the curvature (rotation gradient) tensor is asymmetric and the couple stress moment tensor is symmetric. Laplace and Fourier transform technique is applied to obtain the solutions of the governing equations. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of length scale parameters are depicted graphically on the resulted quantities. Numerical results show that the proposed model can capture the scale effects of microstructures.

• Structural Engineering and Mechanics
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• 제7권2호
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• pp.225-240
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• 1999

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

• Coupled systems mechanics
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• 제11권3호
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• pp.199-215
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• 2022

The present paper deals with the axisymmetric deformation in homogeneousisotropic thermoelastic solid with two temperatures, with and without energy dissipation using modified couple stresstheory. The effect of energy dissipation and two temperature isstudied due to the concentrated normalforce, normalforce overthe circularregion, thermal pointsource and thermalsource over the circular region. The Laplace and Hankel transform techniques have been used to find the solution to the problem. The displacement components, conductive temperature distribution, stress components and couple stress are computed in the transformed domain and further calculated in the physical domain using numerical inversion techniques. Effects of two temperature and energy dissipation on the conductive temperature,stress components and couple stress are depicted graphically.

• Steel and Composite Structures
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• 제45권6호
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• pp.851-863
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• 2022

This research deals with the study of the Thomson heating effect in magneto-thermoelastic homogeneous isotropic rotating medium, influenced by linearly distributed load and as a result of modified couple stress theory. The charge density is taken as a function of the time of the induced electric current. The heat conduction equation with energy dissipation and with hyperbolic two-temperature (H2T) is used to formulate the model of the problem. Laplace and Fourier transforms are used to solve this mathematical model. Various components of displacement, temperature change, and axial stress as well as couple stress are obtained from the transformed domain. To get the solution in physical domain, numerical inversion techniques have been employed. The Thomson effect with GN (Green-Nagdhi) -III theory and Modified Couple Stress Theory (MCST) is shown graphically on the physical quantities.

• Geomechanics and Engineering
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• 제21권5호
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• pp.461-469
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• 2020

The objective of this paper is to study the deformation in a homogeneous isotropic modified couple stress thermoelastic medium with and without energy dissipation and with two temperatures due to thermal source and mechanical force. Laplace and Fourier transform techniques are applied to obtain the solutions of the governing equations. The displacement components, stress components, conductive temperature and couple stress are obtained in the transformed domain. Isothermal boundary and insulated boundary conditions are used to investigate the problem.The effect of two temperature and GN theory of type-II and type-III has been depicted graphically on the various components. Numerical inversion technique has been used to obtain the solutions in the physical domain. Some special cases of interest are also deduced.

• 대한산업공학회지
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• 제17권1호
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• pp.95-108
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• 1991

For the case where the lifetime at a constant stress level has exponential distribution, optimal accelerated life test plans are developed under the assumptions of intermittent inspection and Type I censoring. In a optimal plan, the low and high stress levels, the proportion of test units allocated and the inspection times at each stress are determined such that the asymptotic variance of the maximum likelihood estimator of logarithmic transformed mean at the use condition is minimized. In addition to the optimal plan in which numerical technique to solve the set of nonlinear equations must be employed to determine inspection times at each stress level, we also propose another plans which employ equally-spaced or equal probability inspection schemes at two overstress levels of corresponding optimal one. For both optimal and proposed plans, computational results indicate that the asymptotic variance of the estimated mean at the use stress is insensitive to number of inspections at overstress levels for the range of parameter values considered.