Relaxation characteristics of cement mortar subjected to tensile strain

Tensile relaxation characteristics are important for the crack resistance of concrete members subjected to restrained contraction, for example bonded overlays and patch repairs. In the experimental research discussed in this paper, relaxation characteristics were measured for mortar specimens subjected to constant strain which corresponded to stresses close to the tensile strength of the mortar. Relaxation was found to relieve a considerable portion of tensile stresses. Ultimate relaxation values ranged from 20 to 45%, depending on w/c ratio and specimen age. As expected, a decrease in specimen age and an increase in w/c ratio resulted in increasing relaxation values. The rate of stress decay was found to be rapid, with approximately 80% of the ultimate relaxation occurring in the first 12?h after loading. A basic equation for the prediction of time development of relaxation is proposed and future research needs are discussed.     

Th17 Cells as Potential Probiotic Therapeutic Targets in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) are characterized by wasting and chronic intestinal inflammation triggered by various cytokine-mediated pathways. In recent years, it was shown that T helper 17 (Th17) cells are involved in the pathogenesis of IBD, which makes them an attractive therapeutic target. Th17 cells preferentially produce interleukin (IL)-17A–F as signature cytokines. The role of the interplay between host genetics and intestinal microbiota in the pathogenesis of IBD was demonstrated. Probiotics are live microorganisms that when orally ingested in adequate amounts, confer a health benefit to the host by modulating the enteric flora or by stimulating the local immune system. Several studies indicated the effectiveness of probiotics in preventing and treating IBD (ulcerative colitis, and Crohn’s disease). Furthermore, there is mounting evidence of probiotics selectively targeting the Th17 lineage in the prevention and management of inflammatory and autoimmune diseases such as IBD. This review highlights critical roles of Th17 cells in the pathogenesis of IBD and the rationale for using probiotics as a novel therapeutic approach for IBD through manipulation of Th17 cells. The potential molecular mechanisms by which probiotics modulate Th17 cells differentiation and production are also discussed.     

Steady-State Attainment Period for Fischer–Tropsch Products

In studying the mechanism of the Fischer–Tropsch (FT) reaction, deuterium tracer techniques have been widely used and several important conclusions have been reported. A novel combination of experiment and modelling to quantify the residence times of long chain hydrocarbons using deuterium tracing has been devised. In this study, the effect of variation of residence time with carbon number on the olefin to paraffin ratio is investigated and also the time required for each hydrocarbon to reach steady state is determined. The results show that the olefin to paraffin ratio decreases with increasing carbon number which is consistent with olefin readsorption but not necessarily diffusion enhanced olefin readsorption. Therefore, chain length-dependent solubility in the liquid phase should be the predominant cause for chain length-dependencies of secondary olefin reactions in FT synthesis. Furthermore, the results show that it takes around 100 h for the overall/total mole fractions to reach steady state. Therefore, actual compositions (mole fractions) equilibrate faster even though actual flows (moles/h) might still be changing. Hence, for practical purposes the total mole fraction can be used as a guide to establish steady state.     

The development of an affordable Kgalagadi Sand building block (KSBB)—a position paper

About ¾ of Botswana is covered by Kgalagadi Sands (KS). KS are invariably closely graded, consist of medium to fine sub-rounded particles and contain insignificant amounts of silty and clayey fractions. As a result of these physical and chemical properties, KS lack packing and therefore compactibility, have very high voids ratios and are cohesionless. Consequently, the wet and dry strengths (compressive, shear and flexural), dimensional stability, durability and aesthetics of building blocks moulded with KS alone, in the very rare cases where they occur with silts and clays of the right quantities and quality, are well below acceptable values. This position paper describes the extensive experimental work currently underway at Botswana’s major multi-disciplinary Research and Development (R&;D) Centre—Botswana Technology Centre. The work seeks to render this immensely abundant and widely available, but hitherto unusable resource, utilizable in construction. The affordability of the resultant KSBB shall derive from the local availability of KS as a raw material, usage of locally manufactured manually operated equipment and exploitation of local, largely unskilled labour force under supervision by semi-skilled artisans.     

The role of vapour–liquid equilibrium in Fischer–Tropsch product distribution

This work uses vapour–liquid equilibrium (VLE) to explain the observed two-alpha product distribution in Fischer–Tropsch (FT) reactors. We discuss three possible scenarios or cases of Anderson–Schulz–Flory (ASF) product distribution and VLE. The three cases assume the following: (1) the reaction sets up a single alpha ASF distribution in the total (vapour+liquid) products, (2) the vapour phase follows a single alpha distribution and (3) a single alpha distribution is set up in the liquid phase. We then look at the consequences of these assumptions in conjunction with a simple Raoult's law VLE model on the exit product distributions. We find that only Case 3 gives rise to a two-alpha model in accordance with experimental results that is frequently observed in FT reactors. This model further predicts a relationship between the two values of alpha that are consistent with the measured experimental results.