12 research outputs found
Infection by the castrating parasitic nematode <i>Sphaerularia bombi </i>changes gene expression in <i>Bombus terrestris </i>bumblebee queens
Parasitism can result in dramatic changes in host phenotype, which are themselves
underpinned by genes and their expression. Understanding how hosts respond at the molecular
level to parasites can therefore reveal the molecular architecture of an altered host phenotype.
The entomoparasitic nematode Sphaerularia bombi is a parasite of bumblebee (Bombus) hosts
where it induces complex behavioural changes and host castration. To examine this interaction
at the molecular level, we performed genome-wide transcriptional profiling using RNA-Seq of S.
bombi-infected Bombus terrestris queens at two critical time-points: during and just after
overwintering diapause. We found that infection by S. bombi affects the transcription of genes
underlying host biological processes associated with energy usage, translation, and circadian
rhythm. We also found that the parasite affects the expression of immune genes, including
members of the Toll signaling pathway providing evidence for a novel interaction between the
parasite and the host immune response. Taken together, our results identify host biological
processes and genes affected by an entomoparasitic nematode providing the first steps towards
a molecular understanding of this ecologically important host-parasite interaction
1999 Quadrantids and the lunar Na atmosphere
Enhancements of the Na emission and temperature from the lunar atmosphere
were reported during the Leonids meteor showers of 1995, 1997 and 1998. Here we
report a search for similar enhancement during the 1999 Quadrantids, which have
the highest mass flux of any of the major streams. No enhancements were
detected. We suggest that different chemical-physical properties of the Leonid
and Quadrantid streams may be responsible for the difference.Comment: 5 pages, 1 figure, accepted for publication in MNRA
Probing catalytic surfaces by correlative scanning photoemission electron microscopy and atom probe tomography
The chemical composition and the electronic state of the surface of alloys or mixed oxides with enhanced electrocatalytic properties are usually heterogeneous at the nanoscale. The non-uniform distribution of the potential across their surface affects both activity and stability. Studying such heterogeneities at the relevant length scale is crucial for understanding the relationships between structure and catalytic behaviour. Here, we demonstrate an experimental approach combining scanning photoemission electron microscopy and atom probe tomography performed at identical locations to characterise the surface's structure and oxidation states, and the chemical composition of the surface and sub-surface regions. Showcased on an Ir-Ru thermally grown oxide, an efficient catalyst for the anodic oxygen evolution reaction, the complementary techniques yield consistent results in terms of the determined surface oxidation states and local oxide stoichiometry. Significant chemical heterogeneities in the sputter-deposited Ir-Ru alloy thin films govern the oxide's chemistry, observed after thermal oxidation both laterally and vertically. While the oxide grains have a composition of Ir0.94Ru0.06O2, the composition in the grain boundary region varies from Ir0.70Ru0.30O2 to Ir0.40Ru0.60O2 and eventually to Ir0.75Ru0.25O2 from the top surface into the depth. The influence of such compositional non-uniformities on the catalytic performance of the material is discussed, along with possible engineering levers for the synthesis of more stable and reactive mixed oxides. The proposed method provides a framework for investigating materials of interest in the field of electrocatalysis and beyond
Formation of a 2D Meta stable Oxide by Differential Oxidation of AgCu Alloys
Metal alloy catalysts can develop complex surface structures when exposed to reactive atmospheres. The structures of the resulting surfaces have intricate relationships with a myriad of factors, such as the affinity of the individual alloying elements to the components of the gas atmosphere, and the bond strengths of the multitude of low-energy surface compounds that can be formed. Identifying the atomic structure of such surfaces is a prerequisite for establishing structure-property relationships, as well as for modeling such catalysts in ab initio calculations. Here we show that an alloy, consisting of an oxophilic metal (Cu) diluted into a noble metal (Ag), forms a meta-stable 2-dimensional oxide monolayer the more oxophilic metal, when the alloy is subjected to oxidative reaction conditions. The presence of this oxide is correlated with selectivity in the corresponding test reaction of ethylene epoxidation. In the present study, using a combination of in-situ, ex-situ and theoretical methods (NAP-XPS, XPEEM, LEED, and DFT) we determine the structure to be a 2-dimensional analogue of Cu2O, resembling a single lattice plane of Cu2O. The overlayer holds an pseudo-epitaxial relationship with the underlying noble metal. Spectroscopic evidence shows that the oxideâs electronic structure is qualitatively distinct from its 3-dimensional counterpart, and due to weak electronic coupling with the underlying noble metal, it exhibits metallic properties. These findings provide precise details of this peculiar structure, and valuable insights into how alloying can enhance catalytic properties
Effect of niobium clustering and precipitation on strength of an NbTi-microalloyed ferritic steel
The microstructure-property relationship of an NbTi-microalloyed ferritic steel was studied as a function of thermo-mechanical schedule using Gleeble 3500 simulator, optical and scanning electron microscope, and atom probe tomography