Morphological and ecophysiological root and leaf traits in ectomycorrhizal, arbuscular-mycorrhizal and non-mycorrhizal Alnus incana seedlings

Background and aims The aim was to assess possible benefits or drawbacks of arbuscular-mycorrhizal (AM) and ectomycorrhizal (EM) colonisation compared to no mycorrhizas (NM) in seedlings of the same host species. Eight broadleaf species were tested for mycorrhiza formation. Grey alder (Alnus incana) and four fungal species were selected for further experiments. Methods Grey alder seedlings were inoculated with AM fungi Rhizophagus intraradices and Glomus hoi or EM fungi Paxillus involutus plus an ascomycete isolated from Alnus roots or mock-inoculated (NM). Results EM formed in 70% of root tips and AM in 30% of root length. AM plants were smaller than EM and NM, but their specific root length (SRL) and specific leaf area (SLA) were highest. Net photosynthesis, stomatal conductance and shoot water potential did not differ between treatments. Foliar Ca, K, Mg, Mn, N, P and S concentrations (mg g−1) were highest in AM plants. However, total foliar contents (mg per plant) were lowest in AM plants, except for P, K and Zn. Conclusions The larger SRL and SLA suggest more efficient resource usage in AM plants, even though these were smaller than EM and NM plants. Grey alder is proposed as a new model species for comparisons between mycorrhiza types in cold climates.Peer reviewe

In situ alloying of NiTi : influence of laser powder bed fusion (LBPF) scanning strategy on chemical composition

NiTi alloys are widely used in different industrial and medical applications. Due to the inherent difficulty in the machining of these alloys, the use of Additive Manufacturing (AM) methods has become a popular method for their production. When working with NiTi alloys, there is a requirement on the precise control of their chemical composition, as this determines the phase transition temperatures which are responsible for their shape memory or superelastic behaviour. The high energies used in AM to melt the NiTi alloy leads to nickel evaporation, resulting in a chemical change between the batch powder and the additively manufactured part. Therefore, in AM techniques applied to different NiTi alloys, understanding the relationship between the melting strategy and nickel evaporation is crucial during the developing the desired chemical composition of the final-fabricated material. In this study, three NiTi alloys were fabricated using laser powder bed fusion (LPBF) starting from elementally blended Ni and Ti powders. Different melting strategies, including single and multiple melting, were studied in this work. Remelting improved the density and reduced cracking of the AM part. Microscopic observations, using a Scanning Electron Microscope (SEM) with a Backscattered Electron (BSE) detector, showed that the chemical homogeneity of the materials was enhanced by multiple remelting. Pure Ni and Ti were not found in any of the samples, proving that the applied melting strategies ensured good alloying of both powders. Regardless of the number of melting runs, X-ray diffraction (XRD) analysis showed the presence of NiTi (B2) and (B19′ ) phases, as well as NiTi2, Ni4Ti3 and Ni3Ti precipitates in all samples. The research demonstrated that, during the AM process, and depending on the melting strategy, 1.6–3.0 wt% of nickel evaporates from the material. It was demonstrated that the amount of evaporated nickel increased with the increasing number of melt cycles.peer-reviewe

Heat treatment of NiTi alloys fabricated using laser powder bed fusion (LPBF) from elementally blended powders

The use of elemental metallic powders and in situ alloying in additive manufacturing (AM) is of industrial relevance as it offers the required flexibility to tailor the batch powder composition. This solution has been applied to the AM manufacturing of nickel-titanium (NiTi) shape memory alloy components. In this work, we show that laser powder bed fusion (LPBF) can be used to create a Ni55.7Ti44.3 alloyed component, but that the chemical composition of the build has a large heterogeneity. To solve this problem three different annealing heat treatments were designed, and the resulting porosity, microstructural homogeneity, and phase formation was investigated. The heat treatments were found to improve the alloy’s chemical and phase homogeneity, but the brittle NiTi2 phase was found to be stabilized by the 0.54 wt.% of oxygen present in all fabricated samples. As a consequence, a Ni2Ti4O phase was formed and was confirmed by transmission electron microscopy (TEM) observation. This study showed that pore formation in in situ alloyed NiTi can be controlled via heat treatment. Moreover, we have shown that the two-step heat treatment is a promising method to homogenise the chemical and phase composition of in situ alloyed NiTi powder fabricated by LPBF.peer-reviewe

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements