The Ternary System Nickel-Silicon-Titanium Revisited

International audienceThe constitution of the ternary system Ni-Si-Ti is investigated over the entire composition range using x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), differential scanning thermoanalysis (DTA) and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases tau1-NiSiTi, tau2-Ni4Si7Ti4, tau3-Ni40Si31Ti13, tau4-Ni17Si7Ti6 and tau5-Ni3SiTi2 are corroborated. For the remaining phases the compositions are determined as Ni6Si41Ti53 (tau6), Ni16Si42Ti42 (tau7), and Ni12Si45Ti43 (tau8). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of tau1-NiSiTi, the only congruently melting phase

Reconsidering pluripotency tests: Do we still need teratoma assays?

AbstractThe induction of teratoma in mice by the transplantation of stem cells into extra-uterine sites has been used as a read-out for cellular pluripotency since the initial description of this phenomenon in 1954. Since then, the teratoma assay has remained the assay of choice to demonstrate pluripotency, gaining prominence during the recent hype surrounding human stem cell research. However, the scientific significance of the teratoma assay has been debated due to the fact that transplanted cells are exposed to a non-physiological environment. Since many mice are used for a result that is heavily questioned, it is time to reconsider the teratoma assay from an ethical point of view. Candidate alternatives to the teratoma assay comprise the directed differentiation of pluripotent stem cells into organotypic cells, differentiation of cells in embryoid bodies, the analysis of pluripotency-associated biomarkers with high correlation to the teratoma forming potential of stem cells, predictive epigenetic footprints, or a combination of these technologies. Each of these assays is capable of addressing one or more aspects of pluripotency, however it is essential that these assays are validated to provide an accepted robust, reproducible alternative. In particular, the rapidly expanding number of human induced pluripotent stem cell lines, requires the development of simple, affordable standardized in vitro and in silico assays to reduce the number of animal experiments performed

Uranium-based superconducting materials

Superconductivity has been captivating humankind for more than a century—unimaginable breakthroughs were made and invaluable lessons were learned with perhaps the most important one being that this peculiar phenomenon still holds many surprises. When it comes to actinide-based superconductors, the number of known representatives is rather low. They have small energy scales, which restrict the upper bounds of critical temperatures, i.e., the highly sought-after room-temperature superconductor likely will not be an actinide-based one. However, the study of these peculiar materials can help fully understand what governs the magnitude of the critical temperature in other systems, allowing for a clever avenue toward improvement. In this review, a comprehensive analysis of actinide- and, in particular, uranium-based superconductors is presented, with an emphasis on the chemical bonding and its relation to the observed physical properties. Even more than 60 years after its discovery, the record value of the critical superconducting temperature among uranium-based materials is still being held by U6Fe with Tc = 3.8 K. This is particularly puzzling given much higher critical temperatures of ostensibly similar plutonium- and neptunium-based superconductors. It is therefore reasonable to assume that higher temperature uranium-based superconductors exist, but have not yet been discovered. When it comes to finding new materials and refining features that are responsible for the emergence of superconductivity in these systems, computational analyses are, unfortunately, not yet able to model such complex orbital configurations in a time- and cost-efficient way. The aspiration of this review is that perhaps a thorough empirical analysis can be used to discover new uranium-based superconductors and through this contribute to the general understanding of superconductivity. Due to the limited amount of data on uranium-based systems, just a rough direction is outlined below, with the hope that new members can be discovered and used to refine this approach over time. © 2019 Elsevier B.V