フライアッシュ・セメント系の化学的・力学的特性に及ぼす内部アルカリ活性化の影響

広島大学(Hiroshima University)博士(工学)Doctor of Engineering in Civil and Environmental Engineeringdoctora

Effect of Sodium Sulfate Activator on Compressive Strength and Hydration of Fly-Ash Cement Pastes

In the study, the effect of 4% sodium sulfate (Na2SO4) as an activator on cement pastes with 0%, 20%, and 40% fly-ash replacements and a low water-to-cementitious materials ratio of 0.30 was investigated. The investigation was conducted to evaluate the effectiveness of the technique for the utilization of fly ash in developing sustainable concrete. The use of Na2SO4 decreased setting times of the fresh pastes and increased compressive strength of the hardened pastes up to 28 days irrespective of fly-ash replacement. The use decreased Ca(OH)2 content in the hardened pastes irrespective of fly-ash replacement. Meanwhile, it increased Ca(OH)2 consumption by the pozzolanic reaction of fly ash and content of calcium silicate and aluminate hydrates in the hardened fly-ash–cement pastes. Consequently, the use of Na2SO4 negatively affected cement hydration in the hardened cement pastes without fly ash, while it accelerated ettringite formation and pozzolanic reaction of fly ash in the hardened pastes

The Impact of Job Satisfaction on Job Performance of Tax Officials: An Empirical Study in Vietnam

Purpose: The level of employee satisfaction with the use of e-tax systems is a major factor influencing the success of such systems. While studies typically focus on taxpayers' perspectives, this research investigates the influence of perceived ease of use, IT background, incentives, and social influence on tax officials’ job performance, mediated by tax officials’ job satisfaction.   Theoretical framework: The research is based on the Theory of Planned Behavior (TPB) and Technology Acceptance Model (TAM) to propose the research model which analyze the impact of job satisfaction on job performance.    Design/Methodology/Approach: A quantitative approach was adopted, involving surveys administered to tax officials in Vietnam. The study analyzed 250 valid responses using Cronbach's test, Exploratory Factor Analysis (EFA), Confirmatory Factor Analysis (CFA), and Structural Equation Modeling (SEM).   Findings: The research revealed that all four factors significantly influence job performance through job satisfaction of tax officials in Vietnam. These findings provide valuable insights for tax authorities to improve job performance.   Research, Practical & Social implications: The research results contribute to other countries with similar characteristics in devising strategies to enhance employee performance. However, its limitations include its generalizability to other e-tax systems and countries. Future research with a larger sample size could bolster the applicability of these findings nationally.   Originality/Value: The research suggests tax authorities to support tax officials improve their professional skills; improve the regulations, policies on salary and bonus for tax officials; assist tax officials in using the e-tax system; implement effective communication

Effects of ribosomal exit tunnel on protein's cotranslational folding

In vivo, folding of many proteins occurs during their synthesis in the ribosomeand continues after they have escaped from the ribosomal exit tunnel. Inthis research, we investigate the confinement effects of the ribosome on thecotranslational folding of three proteins, of PDB codes 1PGA, 1CRN and 2RJX,by using a coarse-grained model and molecular dynamics simulation. The exittunnel is modeled as a hollow cylinder attached to a flat wall, whereas aGo-like model is adopted for the proteins. Our results show that theexit tunnel has a strong effect on the folding mechanism by setting an order bywhich the secondary and tertiary structures are formed. For protein 1PGA, thefolding follows two different folding routes. The presence of the tunnel alsoimproves the foldability of protein

Evolution of Protein-protein Interaction Networks in Duplication-Divergence Model

Protein interacts with one another resulting in complex functions in living organisms. Like many other real-world networks, the networks of protein-protein interactions possess a certain degree of ordering, such as the scale-free property. The latter means that the probability $P$ to find a protein that interacts with $k$ other proteins follows a power law, $P(k) \sim k^{-\gamma}$. Protein interaction networks (PINs) have been studied by using a stochastic model, the duplication-divergence model, which is based on mechanisms of gene duplication and divergence during evolution. In this work, we show that this model can be used to fit experimental data on the PIN of yeast Saccharomyces cerevisae at two different time instances simultaneously. Our study shows that the evolution of PIN given by model is consistent with growing experimental data over time, and that the scale-free property of protein interaction network is robust against random deletion of interactions

Effect of surface treatment of recycled concrete aggregate by cement -silica fume slurry on compressive strength of concrete

Recycled concrete aggregate (RCA) used as an alternative to natural aggregate (NA) contains weak adhered mortar. The adhered mortar adversely affects the properties of RCA, and compressive strength of concrete with RCA. Therefore, a treatment method by coating surface of RCA with cement-silica fume slurry (CSS) at concentrations of 20, 40, and 60% was done to evaluate its effects on crushing value and water absorption of RCA, and compressive strength of concrete with treated RCA. The replacements of natural coarse aggregate by RCA for concrete production were 0, 25, and 50% by volume. Compressive strength of the concrete having a constant water-to-cement ratio of 0.35 was tested at ages of 3, 7, 28, and 56 days. Results showed that crushing value and water absorption of the treated RCA were more improved when compared with those of the untreated RCA due to new products formed from cement hydration and pozzolanic reactions on its surface detected by using scanning electron microscope. The surface treatment with CSS at concentration of 60% was the most effective method when compared with that with CSS at concentrations of 20 and 40%. The higher the concentration of CSS, the higher the compressive strength of concrete with the treated RCA. The treatment of RCA led to a significant improvement of compressive strength of the concrete at later ages (i.e., at 28 and 56 days) when compared with the concrete using untreated RCA

Effect of surface treatment of recycled concrete aggregate by cement -silica fume slurry on compressive strength of concrete

Recycled concrete aggregate (RCA) used as an alternative to natural aggregate (NA) contains weak adhered mortar. The adhered mortar adversely affects the properties of RCA, and compressive strength of concrete with RCA. Therefore, a treatment method by coating surface of RCA with cement-silica fume slurry (CSS) at concentrations of 20, 40, and 60% was done to evaluate its effects on crushing value and water absorption of RCA, and compressive strength of concrete with treated RCA. The replacements of natural coarse aggregate by RCA for concrete production were 0, 25, and 50% by volume. Compressive strength of the concrete having a constant water-to-cement ratio of 0.35 was tested at ages of 3, 7, 28, and 56 days. Results showed that crushing value and water absorption of the treated RCA were more improved when compared with those of the untreated RCA due to new products formed from cement hydration and pozzolanic reactions on its surface detected by using scanning electron microscope. The surface treatment with CSS at concentration of 60% was the most effective method when compared with that with CSS at concentrations of 20 and 40%. The higher the concentration of CSS, the higher the compressive strength of concrete with the treated RCA. The treatment of RCA led to a significant improvement of compressive strength of the concrete at later ages (i.e., at 28 and 56 days) when compared with the concrete using untreated RCA