Effect of Supplementary Cementitious Materials on the Compressive Strength and Durability of Short-Term Cured Concrete

This research focuses on studying the effect different supplementary cementitious materials (silica fume, fly ash, slag, and their combinations) on strength and durability of concrete cured for a short period of time—14 days. This work primarily deals with the characteristics of these materials, including strength, durability, and resistance to wet and dry and freeze and thaw environments. Over 16 mixes were made and compared to the control mix. Each of these mixes was either differing in the percentages of the additives or was combinations of two or more additives. All specimens were moist cured for 14 days before testing or subjected to environmental exposure. The freeze–thaw and wet–dry specimens were also compared to the control mix. Results show that at 14 days of curing, the use of supplementary cementitious materials reduced both strength and freeze–thaw durability of concrete. The combination of 10% silica fume, 25% slag, and 15% fly ash produced high strength and high resistance to freeze–thaw and wet–dry exposures as compared to other mixes. This study showed that it is imperative to cure the concrete for an extended period of time, especially those with fly ash and slag, to obtain good strength and durability. Literature review on the use of different supplementary cementitious materials in concrete to enhance strength and durability was also reported

Optimization of FTA technology for large scale plant DNA isolation for use in marker assisted selection

Conventional methods for DNA acquisition and storage require expensive reagents and equipments. Experimental fields located in remote areas and large sample size presents greater challenge to developing country institutions constrained financially. FTATM technology uses a single format utilizing basic tools found in laboratory. In this study, FTATM cards were used to collect over 3000 samples from a field located 130 km and used to screen progeny plants using PCR-marker-assisted selection. PCR product yields and quality are sufficient for reliable scoring, distinguishing heterozygous fromhomozygous plants using ABI 3730 sequencer. Results indicate that this method is faster, easier and in-expensive

Marker assisted introgression of opaque2 gene into herbicide resistant elite maize inbred lines

Marker assisted selection in combination with conventional breeding can greatly accelerate the introgression of modified opaque2 genotype into herbicide resistant maize. By combining these two approaches, time and costs are greatly minimized. The application of opaque2 allele specific SSR markers was done on materials already undergoing selection in a breeding program for converting herbicide resistant maize lines into quality protein maize (QPM) which is the equivalent of modified opaque2 phenotype. The breeder had selected QPM lines using the light table in the previous cycle and we used leaf samples to extract DNA for analysis of the presence of the opaque2 gene using SSR markers. Two co-dominant SSR markers phi057 and umc1066 and a dominant marker phi112 were used. Umc1216, a modifier marker was also tested in combination with the opaque2 markers with theobjective of using the marker to select for modifiers for the opaque2 phenotype. The modified FTA paper technology protocol was applied in field sampling. The results showed 97% of the lines wereopaque2 while 3% were non-opaque2. Both methods of conventional breeding using light table and marker assisted selection (MAS) were comparable. However, the application of SSR markers and theFTA technology offers the breeder a fast, time saving, reliable and less labour intensive method of screening QPM maize during the early growing stages instead of having to wait to screen the kernels onthe light table after harvesting. Moreover, the routine biochemical analysis for high lysine and tryptophan levels need not be carried out at each backcross since the presence of the opaque2 gene is confirmed with markers

Mpemba Effect, Shechtman's Quasicrystals and Students' Exploring Activities

In the 1960s, Tanzanian student Erasto Mpemba and his teacher published an article with the title "Cool" in the journal Physics Education (Mpemba, E. B. - Osborne, D. G.: Cool?. In: Physics Education, vol.4, 1969, pp. 172-175.). In this article they claimed that hot water freezes faster than cold water. The article raised not only a wave of discussions, and other articles about this topic, but also a whole series of new experiments, which should verify this apparent thermodynamic absurdity and find an adequate explanation. Here we give a review with references to explanations and we bring some proposals for experimental student work in this area. We introduce Mpemba Effect not only as a paradoxical physics phenomenon, but we shall present a strong educational message that the Mpemba story brings to the teachers and their students. This message also creates a bridge between this phenomenon and the discovery for which the 2011 Nobel Prize in Chemistry was awarded. It leads to critical adoption of traditional knowledge and encourages resilience in investigative exploration of new things

Structure and stability of steady porous medium convection at large Rayleigh number

A systematic investigation of unstable steady-state solutions of the Darcy–Oberbeck–Boussinesq equations at large values of the Rayleigh number Ra is performed to gain insight into two-dimensional porous medium convection in domains of varying aspect-ratio L. The steady convective states are shown to transport less heat than the statistically steady ‘turbulent’ flow realised at the same parameter values: the Nusselt number Nu∼Ra for turbulent porous medium convection, while Nu∼Ra 0.6 for the maximum heat-transporting steady solutions. A key finding is that the lateral scale of the heat-flux-maximising solutions shrinks roughly as L∼Ra−0.5, reminiscent of the decrease of the mean inter-plume spacing observed in turbulent porous medium convection as the thermal forcing is increased. A spatial Floquet analysis is performed to investigate the linear stability of the fully nonlinear steady convective states, extending a recent study by Hewitt et al. (J. Fluid Mech.737, 2013) by treating a base convective state – and secondary stability modes – that satisfy appropriate boundary conditions along plane parallel walls. As in that study, a bulk instability mode is found for sufficiently small aspect-ratio base states. However, the growth rate of this bulk mode is shown to be significantly reduced by the presence of the walls. Beyond a certain critical Ra-dependent aspect-ratio, the base state is most strongly unstable to a secondary mode that is localised near the heated and cooled walls. Direct numerical simulations, strategically initialised to investigate the fully nonlinear evolution of the most dangerous secondary instability modes, suggest that the (long time) mean inter-plume spacing in statistically-steady porous medium convection results from a balance between the competing effects of these two types of instability

Summary [January 1978]

This brief provides a summary of the world, UK and Scottish economic outlook. The upward movement in the Scotland/UK unemployment relative over the past few quarters is unlikely to portend a return to the poor relative performance of the Scottish economy which occurred in the early nineteen sixties. Nevertheless the outlook for the Scottish economy in 1978 is not very encouraging

Thinking beyond the hybrid:“actually-existing” cities “after neoliberalism” in Boyle <i>et al.</i>

In their article, ‘The spatialities of actually existing neoliberalism in Glasgow, 1977 to present’, Mark Boyle, Christopher McWilliams and Gareth Rice (2008) usefully problematise our current understanding of neoliberal urbanism. Our response is aimed at developing a sympathetic but critical approach to Boyle et al's understanding of neoliberal urbanism as illustrated by the Glasgow example. In particular, the counterposing by Boyle et al of a 'hybrid, mutant' model to a 'pure' model of neoliberalism for us misrepresents existing models of neoliberalism as a perfectly finished object rather than a roughly mottled process. That they do not identify any ‘pure’ model leads them to create a straw construct against which they can claim a more sophisticated, refined approach to the messiness of neoliberal urbanism. In contrast, we view neoliberalism as a contested and unstable response to accumulation crises at various scales of analysis