• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.15-22
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• 2003

The appropriate description of the stress-anisotropy and time-dependent behavior of cohesive soils is very important in representing the real soil behavior. In this study, two constitutive relations have been incorporated based on the generalized viscous theory: one is the plastic constitutive relation adopted to capture the stress-anisotropy with a few model parameters; the other is the rate-dependent constitutive relation adopted to describe the strain rate-dependent behavior, an important time-dependent behavior in cohesive soils. The incorporated and proposed constitutive model has relatively a few model parameters and their values need not to be re-evaluated at different strain rates. The proposed model has been verified and investigated with the anisotropic triaxial test results obtained by using the artificial homogeneous specimens.

• Journal of the Korean Data and Information Science Society
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• v.24 no.4
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• pp.877-883
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• 2013

The quadratic inference functions (QIF) method proposed by Qu et al. (2000) and the generalized method of moments (GMM) for marginal regression analysis of longitudinal data with time-dependent covariates proposed by Lai and Small (2007) both are the methods based on generalized method of moment (GMM) introduced by Hansen (1982) and both use generalized estimating equations (GEE). Lai and Small (2007) divided time-dependent covariates into three types such as: Type I, Type II and Type III. In this paper, we compared these methods in the case of Type II and Type III in which full covariates conditional mean assumption (FCCM) is violated and interested in whether they can improve the results of GEE with independence working correlation. We show that in the marginal regression model with Type II time-dependent covariates, GMM Type II of Lai and Small (2007) provides more ecient result than QIF and for the Type III time-dependent covariates, QIF with independence working correlation and GMM Type III methods provide the same results. Our simulation study showed the same results.

• Computers and Concrete
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• v.23 no.2
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• pp.133-143
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• 2019

The paper presents the experimental investigations into the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent tensile strength of concrete. The splitting and flexural tensile strength of concrete was determined at the ages of 3, 7, 28, 56, 90, 150 and 180 days using the cylindrical and prism specimens respectively for plain and GGBFS concrete. The amount of cement replacement by GGBFS was 0%, 40% and 60% on the weight basis. The maximum curing age was kept as 28 days. The results showed that the splitting and flexural tensile strength of concrete containing GGBFS has been found lower than the plain concrete at all ages and for all mixes. The tensile strength of 40 percent replacement has been found higher than the 60 percent at all ages and for all mixes. The rate of gain of splitting and flexural tensile strength of 40 percent GGBFS concrete is found higher than the plain concrete and 60 percent GGBFS concrete at the ages varying from 28 to 180 days. The experimental results of time-dependent tensile strength of concrete are compared with the available models. New models for the prediction of time-dependent splitting and flexural tensile strength of concrete containing GGBFS are proposed. The present experimental and analytical study will be helpful for the designers to know the time-dependent tensile properties of GGBFS concrete to meet the design requirements of liquid retaining reinforced and pre-stressed concrete structures.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.2
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• pp.80-88
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• 2017

In this research a time dependent thermal and solutal convection was computationally investigated for the physical vapor transport of the mixture of $Hg_2Cl_2-I_2$ system with for the convective regime from thermal Rayleigh number of $2.16{\times}10^6$ up to $1.7{\times}10^7$ with marching time to a steady state problem. With time marching, the convective cells are decreased for the thermal Rayleigh number of $2.16{\times}10^6$, and increased for the thermal Rayleigh number of $1.7{\times}10^7$. The convective flow structures are found to be essentially time independent on the horizontal orientation of the enclosure with respect to the gravity vector, and on the other hand, time dependent on the vertical orientation of the enclosure with respect to the gravity vector.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.3861-3878
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• 2021

The steady-state simplified spherical harmonics equations (SP_N equations) are a higher order approximation to the neutron transport equations than the neutron diffusion equation that also have reasonable computational demands. This work extends these results for the analysis of transients by comparing of two formulations of time-dependent SP_N equations considering different treatments for the time derivatives of the field moments. The first is the full system of equations and the second is a diffusive approximation of these equations that neglects the time derivatives of the odd moments. The spatial discretization of these methodologies is made by using a high order finite element method. For the time discretization, a semi-implicit Euler method is used. Numerical results show that the diffusive formulation for the time-dependent simplified spherical harmonics equations does not present a relevant loss of accuracy while being more computationally efficient than the full system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2D
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• pp.185-192
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• 2011

More practical outputs and insights can be obtained through transportation analysis considering the time-dependent traffic movements. This study proposes a method of constructing time-dependent O-D trip tables for expressway corridor using real-world individual trip data. In this study, time-dependent O-D trip tables for the nationwide highway network are constructed based on toll collection system data. The proposed methodology is to convert nationwide time-dependent O-D trip tables into Korean expressway corridor O-D trip tables in order to deal with the computational complexity arising from simulating a large-scale traffic network. The experiment results suggest that actual individual trip record data can be used to effectively construct time-dependent O-D trip tables. They also imply that the construction of time-dependent O-D trip tables for the national highway networks along with those for Korean expressway developed in this study would make transportation analysis more practical and applicable to real-time traffic operation and control.

• Structural Engineering and Mechanics
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• v.38 no.2
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• pp.171-193
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• 2011

One of the possible alternatives of simulation-based time-dependent reliability assessment of pre-stressed biconcave and biconvex cable trusses, the Monte Carlo method, is applied in this paper. The influence of an excessive deflection of cable truss (caused by creep of cables and rheologic changes) on its time-dependent serviceability is investigated. Attention is given to the definition of the basic random variables and their statistical functions (basic, mutually dependent random variables such as the pre-stressing forces of the bottom and top cable, structural geometry, the Young's modulus of elasticity of the cables, and the independent variables, such as permanent load, wind, snow and thermal actions). Then, the determination of the response of the cable truss to the loading effects, and the definition of the limiting values considering serviceability of the structure are performed. The potential of the method, using direct Monte Carlo technique for simulation-based time-dependent reliability assessment as a powerful tool, is emphasized. Results obtained by the First order reliability method (FORM) are compared with those obtained by the Monte Carlo simulation technique.

• The Korean Journal of Applied Statistics
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• v.35 no.1
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• pp.35-47
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• 2022

The receiver operating characteristic (ROC) curve was developed to quantify the classification ability of marker values (covariates) on the response variable and has been extended to survival data with diverse missing data structure. When survival data is understood as binary data (status of being alive or dead) at each time point, the ROC curve expressed at every time point results in time-dependent ROC curve and time-dependent area under curve (AUC). In particular, a follow-up study brings the change of cohort and incomplete data structures such as censoring and competing risk. In this paper, we review time-dependent ROC estimators under several contexts and perform simulation to check the performance of each estimators. We analyzed a dementia dataset to compare the prognostic power of markers.

• Journal of the Chungcheong Mathematical Society
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• v.31 no.3
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• pp.287-308
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• 2018

This paper deals with blow-up phenomena for an initial boundary value problem of a quasilinear parabolic equation with time-dependent coefficient in a bounded star-shaped region under nonlinear boundary flux. Using the auxiliary function method and differential inequality technique, we establish some conditions on time-dependent coefficient and nonlinear functions for which the solution u(x, t) exists globally or blows up at some finite time $t^*$. Moreover, some upper and lower bounds for $t^*$ are derived in higher dimensional spaces. Some examples are presented to illustrate applications of our results.