This paper studies a single machine scheduling problem with time-dependent learning and setup times. Time-dependent learning means that the actual processing time of a job is a function of the sum of the normal proces...This paper studies a single machine scheduling problem with time-dependent learning and setup times. Time-dependent learning means that the actual processing time of a job is a function of the sum of the normal processing times of the jobs already scheduled. The setup time of a job is proportional to the length of the already processed jobs, that is, past-sequence-dependent (psd) setup time. We show that the addressed problem remains polynomially solvable for the objectives, i.e., minimization of the total completion time and minimization of the total weighted completion time. We also show that the smallest processing time (SPT) rule provides the optimum sequence for the addressed problem.展开更多
A computer-based model and method was presented to predict the time dependency of chloride diffusion coefficients in cement paste. The HYMOSTRUC3D model was applied to generate a 3D representative elementary volume （...A computer-based model and method was presented to predict the time dependency of chloride diffusion coefficients in cement paste. The HYMOSTRUC3D model was applied to generate a 3D representative elementary volume （REV） of cement paste. In the simulation of microstructure, both of cement hydration and chloride binding were considered. With the simulated microstructure of cement paste, the finite element method was applied to simulate the diffusion process of chloride through the saturated cement paste. Based on the Fick’s first law, the chloride diffusion coefficient can be calculated. In this method, the influences of age and w/c ratio on the chloride diffusion coefficient were evaluated. The simulated chloride diffusivities with various w/c at different time were compared to experimental data obtained from the literature. The experimental results indicate that the chloride diffusion coefficient decreases with the increase of time and the decrease of w/c ratio. The trend of simulated relationship （diffusion coefficient vs time, diffusion coefficient vs w/c ratio） fits very well with the experiments.展开更多
As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, Li Al-LDHs was obtained by a hydrothermal method. In order to ...As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, Li Al-LDHs was obtained by a hydrothermal method. In order to investigate the effects of Li Al-LDHs on the early hydration of calcium sulphoaluminate（CSA） cement paste, compressive strength, setting time and hydration heat were tested while X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR）, scaning electron microscopy（SEM） and differential scanning calorimetry（DSC） analysis were employed. The results indicated that Li Al-LDHs could significantly improve the early compressive strength and shorten the setting time of calcium sulphoaluminate cement paste with 3 wt% concentration. Besides, the hydration exothermic rate within 5h was accelerated with increasing Li Al-LDHs content. Moreover, the addition of Li Al-LDHs did not result in the formation of a new phase, but increased the quantity of hydration products providing higher compressive strength, shorter setting time and denser microstructure.展开更多
文摘This paper studies a single machine scheduling problem with time-dependent learning and setup times. Time-dependent learning means that the actual processing time of a job is a function of the sum of the normal processing times of the jobs already scheduled. The setup time of a job is proportional to the length of the already processed jobs, that is, past-sequence-dependent (psd) setup time. We show that the addressed problem remains polynomially solvable for the objectives, i.e., minimization of the total completion time and minimization of the total weighted completion time. We also show that the smallest processing time (SPT) rule provides the optimum sequence for the addressed problem.
文摘A computer-based model and method was presented to predict the time dependency of chloride diffusion coefficients in cement paste. The HYMOSTRUC3D model was applied to generate a 3D representative elementary volume （REV） of cement paste. In the simulation of microstructure, both of cement hydration and chloride binding were considered. With the simulated microstructure of cement paste, the finite element method was applied to simulate the diffusion process of chloride through the saturated cement paste. Based on the Fick’s first law, the chloride diffusion coefficient can be calculated. In this method, the influences of age and w/c ratio on the chloride diffusion coefficient were evaluated. The simulated chloride diffusivities with various w/c at different time were compared to experimental data obtained from the literature. The experimental results indicate that the chloride diffusion coefficient decreases with the increase of time and the decrease of w/c ratio. The trend of simulated relationship （diffusion coefficient vs time, diffusion coefficient vs w/c ratio） fits very well with the experiments.
基金Supported by the National Natural Science Foundation of China （1097178） the Project of Creative Team by the Mimstry of Education of China （IRT0856） the Natural Science Foundation of the Education Department of Shaanxi Province （09JK590）
基金Funded by the National Natural Sciense Foundation of China(No.51272068)
文摘As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, Li Al-LDHs was obtained by a hydrothermal method. In order to investigate the effects of Li Al-LDHs on the early hydration of calcium sulphoaluminate（CSA） cement paste, compressive strength, setting time and hydration heat were tested while X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR）, scaning electron microscopy（SEM） and differential scanning calorimetry（DSC） analysis were employed. The results indicated that Li Al-LDHs could significantly improve the early compressive strength and shorten the setting time of calcium sulphoaluminate cement paste with 3 wt% concentration. Besides, the hydration exothermic rate within 5h was accelerated with increasing Li Al-LDHs content. Moreover, the addition of Li Al-LDHs did not result in the formation of a new phase, but increased the quantity of hydration products providing higher compressive strength, shorter setting time and denser microstructure.
