• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.259-268
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• 2016

The service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack can be classified into deterministic and probabilistic method, and it significantly varies with design parameters. The present work derives PDF (Probability of Durability Failure) and the related service life considering time-dependent diffusion coefficient and internal parameters such as reference diffusion coefficient, critical chloride content, and time-exponent. When critical chloride content increases to 133.3%, the changing ratios of service life are 134.0~145.4% for deterministic method and 149.2%~152.5% for probabilistic method, respectively. In the case of increasing time-exponent to 200%, they increase to 323.8% for deterministic method and 346.0% for probabilistic method. Through adopting time-diffusion coefficient for probabilistic method, reasonable service life evaluation can be achieved, and it is also verified that increasing time-exponent through mineral admixture is very effective to extension of service life in RC structure.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.4
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• pp.363-373
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• 2006

Statement of Problem : The accuracy and dimensional stability of elastomeric impression materials have been the subject of numerous investigation. Few studies have addressed the effect of changes in time on the dimensional stability of impression materials. Purpose: The purpose of this investigation was to evaluate the effects of elastomeric impression materials and storage time on dimensional stability. Materials and methods: A total of 75 impressions were made of epoxy resin dies mimicked prepared 3-unit fixed partial denture. The dies had 1 buccolingual, 1 mesiodistal and 1 occlusogingival lines and interpreped dot. Impression materials investigated included two polyether impression materials and three polyvinylsiloxane impression material. 15 specimens were made of each impression material and poured by type IV stone over times (30 minutes, 24 hours, 72 hours) after mixing; the same examiner measured each specimen 3 times at a magnification of 3.5$\times$. All statistical tests were performed with the level of significance set at .05. Results : The results indicated that significant difference at any measuring point of stone dies of the polyether impression materials and when measurements at 30 minutes, 24 hours, and 72 hours were compared ; the length of measuring point increased significantly as time passed by. However this result is not significant clinically. Analysis also showed significant differences at any measuring point when polyvinylsiloxane and polyether impression materials were compared and significant differences clinically. Conclusion: Under the conditions of this study, the shrinkage rate of the polyvinylsiloxane and polyether impression materials significantly increased as time passed by. The polyether impression materials showed higher shrinkage significantly, while the shrinkage rate of all five materials showed a significant time-dependent increase.

• Biomaterials and Biomechanics in Bioengineering
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• v.3 no.2
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• pp.105-114
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• 2016

The purpose of this study is to evaluate the effects of cryopreservation on dental pulp-derived stem cells (DPSC) viability over a period of three years. Dental pulp-derived stem cells were isolated and cultured from thirty-one healthy teeth. DPSC isolates were assessed for doubling-time and baseline viability prior to cryopreservation and were assessed again at three time points; one week (T1), 18 months (T2), and 36 months (T3). DPSC can be grouped based on their observed doubling times; slow (sDT), intermediate (iDT), and rapid (rDT). Viability results demonstrated all three types of DPSC isolates (sDT, iDT and rDT) exhibit time-dependent reductions in viability following cryopreservation, with the greatest reduction observed among sDT-DPSCs and the smallest observed among the rDT-DPSC isolates. Cryopreserved DPSCs demonstrate time-dependent reductions in cellular viability. Although reductions in viability were smallest at the initial time point (T1) and greatest at the final time point (T3), these changes were markedly different among DPSC isolates with similar doubling times (DTs). Furthermore, the analysis of various DPSC biomarkers - including both intracellular and cell surface markers, revealed differential mRNA expression. More specifically, the relative high expression of Sox-2 was only found only among the rDT isolates, which was associated with the smallest reduction in viability over time. The expression of Oct4 and NANOG were also higher among rDT isolates, however, expression was comparatively lower among the sDT isolates that had the highest reduction in cellular viability over the course of this study. These data may suggest that some biomarkers, including Sox-2, Oct4 and NANOG may have some potential for use as biomarkers that may be associated with either higher or lower cellular viability over long-term storage applications although more research will be needed to confirm these findings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.269-279
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• 1994

This paper concentrates on the finite element analysis of concrete structures considering the material nonlinearity and time-dependent structural behavior. Using the rotating crack model among the smeared cracking model, the structural behavior up to ultimate load is simulated, and concrete is assumed to be an orthotropic material. Especially to include the tension stiffening effect in bending behavior, a criterion based on the fracture mechanics concept is introduced and the numerical error according to the finite element mesh size can be minimized through the application of the proposed criterion. Besides, the governing equation for steel is systematized by embeded model to cope with the difficulty in modeling of complex geometry. Finally, to trace the structural behavior with time under cracked and/or uncracked section, an algorithm for the purpose of time-dependent analysis is formulated in plane stress-strain condition by the age-adjusted effective modulus method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1494-1501
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• 2006

Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600$^{\circ}C$. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400$^{\circ}C$, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400$^{\circ}C$ while stress-strain curve is changed at 500$^{\circ}C$ as the strain rate is changed. Creep tests were conducted at 250$^{\circ}C$ and 500$^{\circ}C$ and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.

• YAKHAK HOEJI
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• v.44 no.6
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• pp.558-565
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• 2000

SK-1080 is one of the newly developed orally active nonpeptide angiotensinII $AT_1-receptor$ antagonist that selectively acts at $AT_1$ receptor with high affinity. The cardiac effect on ischemia/reperfusion injury of SK-1080 was compared with those of losartan, a prototype of this class, in isolated rat hearts. Isolated perfused rat heart was pretreated with drug for 10 min and then subjected to global ischemia for 30 min followed by reperfusion with- or without drug for 30 min. The possible additive effect of SK-1080 on the platelet aggregation and coagulation in human blood was also studied. We investigated whether SK-1080 effects the platelet aggregation induced by ADP, a platelet agonist partially dependent on $thromboxaneA_2$. The clotting times in the prothrombin time (PT) and activated partial thromboplastin time (APTT) were also examined in human plasma in vitro as coagulation screening test. SK-1080 improved reperfusion function (LVDP, left ventricular developed pressure; PRP, rate-pressure product) in a dose-dependent manner. SK-1080 reduced ADP-induced platelet aggregation compared with vehicle but less than losartan, and did not affect clotting times.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.291-299
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• 2003

The effect of temperature and soil confining stress on geosyntheic creep behaviour was studied by performing the temperature dependent confined creep tests for HDPE geogrid and geomembrane specimen. The visco-elastic creep coefficients of the geosynthetics were evaluated by the test results and it was proposed that the simple expressions for the instantaneous and limit creep strain of geosynthetics was considered as a function of temperature and confining stress on geosynthetics. Based on the time-temperature superposition principle, a master curve has been drawn for extrapolating tensile creep strains to longer time intervals(1$\times$10 $^7$min.∼1$\times$10$^{10}$min.). By using this master curves, the shift factors which can be used in establishing master curve considering confining stress on geosynthetics were carried out. Each tests was performed during 8,000∼12,000 min., with temperature ranging between 5$^{\circ}C$ and 4$0^{\circ}C$ and with confining stress ranging between 0 t/$m^2$ and 9 t/$m^2$.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2003.11a
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• pp.82-82
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• 2003

The present study was undertaken to examine the cytotoxic effect of extract of Eurya emarginata against cancer cells and to develop an anti-cancer agent using components of its leaves. The crude extract of its leaves markedly inhibited the growth of leukemia cells including HL-60. When the HL-60 cells were treated with the extract, DNA fragmentation, morphologic changes and sub-Gl hypodiploid cells were observed. Therefore, the inhibitory effect of E. emarginata on the growth of the HL-60 cells appears to arise from the induction of apoptosis. Moreover, the extract markedly reduced c-Myc expression in a time-dependent manner. Eutigoside C showing the cytotoxic effect was isolated from the leaves of E. emarginata. Eutigoside C reduced the Bcl-2 protein and mRNA levels in a time-dependent manner, whereas the Bax protein and mRNA expression levels were slightly increased. When HL-60 cells were treated with eutigoside C, the release of cytochrome C from mitochondria into the cytosol was observed. Also, the expressions of the active forms of caspase 9 and 3 were increased and the activation of caspase 3 was demonstrated by the cleavage of Poly(ADP-ribose) polymerase, a vital substrate of effector caspase. The results indicate that the eutigoside C from E. emarginata induce apoptosis of HL-60 cells via the down-regulation of Bcl-2 expression and activation of caspases.

• Journal of Distribution Science
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• v.18 no.8
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• pp.113-125
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• 2020

Purpose: The purpose of this paper is to investigate the effect of interaction between product category (fresh vs. indulgent product) and shopping options (shipping charge and delivery time) on customer satisfaction and purchase intent in an e-commerce context. When ordering groceries online, consumers begin to allocate a larger share of their grocery budget toward product categories that generally contain healthier items at the expense of product categories that generally contain more indulgent products. Moreover, customers are extremely sensitive to shipping options such as shipping charges and delivery time. Therefore, this research investigates the issue at a more segmented level to focus on the impact that one dimension of logistics service quality - product category, shipping charge, and delivery time have on customer satisfaction and purchase intent. Research design, data, and methodology: To test the theoretically derived priori hypotheses concerning product category, shipping charges, delivery time, satisfaction, and purchase intent, this research presented a scenario-based experiment. Eight treatment groups were assigned by the method of product category (fresh produce vs. indulgent product), shipping charge (free vs. paid), and delivery time (one-day vs. two to three days). A total of 240 subjects were divided into groups and exposed to one of the eight scenarios. Participant's purchase intention was the dependent variable, and ANOVA and L-matrix were used to analyze for main and interactive effects between factors. Conclusions: Results indicated that in tests 1 and 2, free shipping and fast delivery time increased consumer satisfaction as well as purchase intent, and fast delivery moderated the impact of free shipping on consumer satisfaction and purchase intent. Test 3 showed that the effect of free shipping on consumer satisfaction and purchase intent moderated by fast delivery for indulgent products. In contrast, fast delivery for fresh products moderated the effect of paid shipping on consumer satisfaction and purchase intent. Consistent with this proposed mechanism, the relative importance of fresh produce versus indulgent products highlights the effect of shipping options on consumer satisfaction and purchase intent when ordering the target product in an e-commerce context. We conclude with a discussion of the theoretical and practical implications of our findings.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.83-91
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• 2015

With varying conditions of concrete surface, induced chloride contents are changed and this is a key parameter for steel corrosion and service life in RC (Reinforced Concrete) structures. Many surface enhancement techniques using impregnation have been developed, however the evaluation techniques for chloride behavior through doubly layered media and time-dependent diffusion are rarely proposed. This paper presents an analysis technique considering double-layer concrete and time-dependent diffusion behavior, and the results are compared with those from the previous test results through reverse analysis. The chloride profiles from the surface-impregnated concrete exposed to atmospheric, tidal, submerged zone for 2 years are adopted. Furthermore surface chloride contents and diffusion coefficients are obtained, and are compared with those from Life365. Through consideration of time effect, the relative error decreases from 0.28 to 0.20 in atmospheric, 0.29 to 0.11 in tidal, and 0.54 to 0.40 in submerged zone, respectively, which shows more reasonable results. Utilizing the diffusion coefficients from Life365, relative errors increases and it needs deeper penetration depth (e) and lower diffusion coefficient ratio ($D_1/D_2$) due to higher diffusion coefficient.