Search results for " industry."
showing 10 items of 2285 documents
Porous structure and mechanical strength of cement-lime pastes during setting
2015
Abstract The acceleration of a cement paste setting as a result of lime addition may be shown from isothermal calorimetry measurements. We investigated the underlying mechanisms through two techniques that provide information on porous structure (using Nuclear Magnetic Resonance) and mechanical properties (elastic modulus measured by rheometry). The correlation of the two sets of results on a cement paste clearly reveals the successive steps of setting, and particularly highlights the so-called induction period. We show that this induction period disappears in the presence of lime, leading to an acceleration of the setting. We also show that beyond some critical concentration of added lime …
Prediction of Long-Term Chemical Evolution of a Low-pH Cement Designed for Underground Radioactive Waste Repositories
2012
Low-pH cements, also referred as low-alkalinity cements, are binders with a pore solution pH ≤ 11. They can be designed by replacing significant amounts of Portland cement (OPC) (≥40 %) by silica fume, which can be associated in some cases to low-CaO fly ash and/or ground granulated blast furnace slag to decrease the heat output during hydration by dilution of OPC and improve the mechanical strength of the final material. With the prospect of using these materials in a geological repository, it is of main importance to estimate their long-term properties and the influence of external and internal factors (chemical composition of the binder, storage temperature) on their characteristics. For…
Cement selection criteria for full coverage restorations: A comprehensive review of literature
2021
Background Proper cement selection in fixed prosthesis plays a determinative role in providing long-term serviceability, retention, caries prevention, and patient satisfaction. This study, reviews different luting agent characteristics and their application based on different clinical situations and different types of full coverage restorations. Material and methods An electronic search was conducted through PubMed, Medline, and Google scholar using following keywords or combinations: restoration, full coverage, PFM, porcelain fused to metal, all ceramic, zirconia, ceramic, casting, fixed partial denture, cement*, dental cement, cement selection, and retention. The most related articles wer…
Retention of alkali ions by hydrated low-pH cements: Mechanism and Na+/K+ selectivity
2013
Low-pH cements, also referred to as low-alkalinity cements, can be designed by replacing significant amounts of Portland cement by pozzolanic materials. Their pore solution is characterized by a pH near 11, and an alkali concentration much lower than that of Portland cement. This work investigates the retention of sodium and potassium by a hydrated low-pH cement comprising 60% Portland cement and 40% silica fume. It is shown that sorption of potassium is higher than that of sodium and mainly results from counterion charge balancing of the C-S-H negative surface charge. To explain the greater retention of potassium compared to sodium, it is postulated that potassium, unlike sodium, may enter…
Comparison of simultaneous saccharification and fermentation and separate hydrolysis and fermentation processes for butanol production from rice straw
2020
Abstract Rice straw (RS) is one of the lignocellulosic wastes with the highest global production. The main objective of this study was to maximise the butanol production by Clostridium beijerinckii DSM 6422 from RS pretreated by microwave-assisted hydrothermolysis. Two different fermentation strategies were compared: separate hydrolysis and fermentation (SHF, two-step process) and simultaneous saccharification and fermentation (SSF, one-step process). In parallel, the variables that significantly affected the butanol production were screened by using fractional factorial designs. Butanol concentration and productivity at 48 h were, respectively, 8% and 173% higher in SSF than in SHF. A one-…
Safety culture assessment in high reliability organizations: the use of questionnaires in the nuclear industry
2017
El objetivo principal de esta tesis es proporcionar una visión general de las formas actuales de entender, tratar, y evaluar la cultura de la seguridad (poniendo un énfasis particular en la industria nuclear y en la utilización de cuestionarios), y proporcionar orientación a los investigadores y profesionales sobre cómo capturar la cultura de seguridad de las centrales nucleares. Para ello, la tesis actual incluye los siguientes capítulos: CAPÍTULO I - Se presenta una breve introducción a la industria nuclear. Asimismo se presentan algunos de los más destacables pros y contras de la energía nuclear, y desafíos importantes a los que la industria nuclear se estado enfrentando en los últimos a…
The transformation of the Russian defence industry
1995
TRADITIONALLY, THE DEFENCE INDUSTRY constituted the most powerful industrial lobby in the USSR, with an administrative structure at all the organisational levels where its interests could be affected. With a hierarchical and pyramidal structure, the different entities of the sector remained isolated from strictly civilian bodies. The strategic part it played within the organisation of the Soviet Union enabled the defence industry to manage a growing and important volume of resources; on the one hand, it had a special supply system which guaranteed regular high-quality provision of the most advanced technology in the country, as well as highly qualified human resources. On the other hand, th…
Microstructure and mechanical effects of spark plasma sintering in alumina monolithic ceramics
2013
The specific effects of spark plasma sintering (SPS) on the creep behavior, microstructure and mechanical properties of alumina monolithic ceramic were investigated. SPS introduces strains that concentrate at grain boundaries and inhibit crack growth, resulting in an improvement in the flexural strength and fracture toughness. However, creep blocks grain boundary movements and decreases the reliability of the material. These strains can be removed by a post-sintering thermal treatment, which plays an important role in the distribution of dislocations.
Microbial diversity of traditional Sicilian cheeses
2017
In the last years, the microbial characterisation of traditional Sicilian cheeses, such as Caciocavallo Palermitano, Protected Designation of Origin (PDO) Pecorino Siciliano and PDO Vastedda della valle del Belìce have been the object of different studies conducted by our research group. To this purpose, the aim of the present study was to describe the microbial population of traditional Sicilian cheeses.
Mixed monolayers of natural and polymeric phospholipids: structural characterization by physical and enzymatic methods
1990
This study has focused on physical characterization and enzymatic hydrolysis of mixed monolayers of a natural phospholipid substrate and a polymerizable phospholipid analogue. Such a mixed system presents the possibility to stabilize model biomembranes, vary the molecular environment within the layer through polymerization and simultaneously examine these influences on monolayer structure. Phospholipase A2 was used here as a sensitive probe of the molecular environment within these mixed, polymerizable monolayers to complement information obtained from isotherm and isobar data. The results clearly show a strong influence of molecular environment on phospholipase A2 activity, even if differe…