Search for: All records

Although analogical examples can support better understanding of new science concepts, when analogies are included superficially and without explanation they may have unintended negative effects. In this study, simple inclusion of analogies greatly increased the perceived familiarity and predicted understanding of geology concepts. Higher judgements of familiarity and predicted understanding could produce illusions of understanding when reading texts about these concepts. 

Although analogical examples can support better understanding of new science concepts, when analogies are included superficially and without explanation they may have unintended negative effects. In this study, simple inclusion of analogies greatly increased the perceived familiarity and predicted understanding of geology concepts. Higher judgements of familiarity and predicted understanding could produce illusions of understanding when reading texts about these concepts. 

Lightweight automotive extrusions are increasingly complex, thin-walled, multi-hollow profiles made from high-strength, quench-sensitive aluminum alloys such as AA6082. These alloys require rapid quenching as the profile leaves the press to prevent the precipitation of undesired phases, to create a supersaturated solid solution, and to prepare them for subsequent age-hardening treatments; e.g., for the T6 temper. However, rapid quenching can cause profile distortion, which leads to high scrap reject rates, increasing costs, environmental impacts, and production lead time. This study tests two hypotheses: (1) That the different cooling rates set-up across the profile section during quenching induces not only distortion but also varying mechanical properties across the section; and (2) That this temperature differential can be minimized by combining (conventional) external quenching with internal quenching supplied by through-die cooling channels. The first hypothesis is tested experimentally by taking tensile specimens from different locations of an AA6082 multi-hollow profile, showing a significant decrease in the ductility and ultimate tensile strength of samples extracted from internal webs. The second hypothesis is tested by performing thermo-mechanical finite element simulations that compare the thermal history, stresses, and strains of simultaneous internal and external quenching in contrast with conventional quenching (external only). The combined quenching approach results in a significant reduction in the residual stress and plastic deformation. This implies lower scrap reject rates, improved internal wall mechanical properties (giving scope for further light-weighting), and a wider profile design space by enabling the extrusion of more challenging profile shapes. 

Mycobacterium tuberculosis ( Mtb ) has complex and dynamic interactions with the human host, and subpopulations of Mtb that emerge during infection can influence disease outcomes. This study implicates zinc ion (Zn 2+ ) availability as a likely driver of bacterial phenotypic heterogeneity in vivo . Zn 2+ sequestration is part of “nutritional immunity”, where the immune system limits micronutrients to control pathogen growth, but this defense mechanism seems to be ineffective in controlling Mtb infection. Nonetheless, Zn 2+ -limitation is an environmental cue sensed by Mtb , as calprotectin triggers the zinc uptake regulator (Zur) regulon response in vitro and co-localizes with Zn 2+ -limited Mtb in vivo . Prolonged Zn 2+ limitation leads to numerous physiological changes in vitro , including differential expression of certain antigens, alterations in lipid metabolism and distinct cell surface morphology. Furthermore, Mtb enduring limited Zn 2+ employ defensive measures to fight oxidative stress, by increasing expression of proteins involved in DNA repair and antioxidant activity, including well described virulence factors KatG and AhpC, along with altered utilization of redox cofactors. Here, we propose a model in which prolonged Zn 2+ limitation defines a population of Mtb with anticipatory adaptations against impending immune attack, based on the evidence that Zn 2+ -limited Mtb are more resistant to oxidative stress and exhibit increased survival and induce more severe pulmonary granulomas in mice. Considering that extracellular Mtb may transit through the Zn 2+ -limited caseum before infecting naïve immune cells or upon host-to-host transmission, the resulting phenotypic heterogeneity driven by varied Zn 2+ availability likely plays a key role during early interactions with host cells.