First findings of impact melt in the IIE Netschaëvo meteorite

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Occurrence of Siliceous Impact Melt in Netschaëvo IIE? A FIB-TEM Study

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Immiscible silicate liquids and phosphoran olivine in Netschaëvo IIE silicate: Analogue for planetesimal core–mantle boundaries

We have investigated a piece of the Netschaëvo IIE iron meteorite containing a silicate inclusion by means of electron microprobe analysis (EMPA) and transmission electron microscopy (TEM). Netschaëvo contains chondrule-bearing clasts and impact melt rock clasts were also recently found. The examined inclusion belongs to the latter and is characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a hyaline matrix. This matrix material has a quasi-basaltic composition in the inner part of the inclusion, whereas the edge of the inclusion has a lower SiO2 concentration and is enriched in MgO, P2O5, CaO, and FeO. Close to the metal host, the inclusion also contains euhedral Mg-chromite crystals and small (<2 μm), Si-rich globules. A TEM foil was cut from this glassy, silico-phosphate material. It shows that the material consists of elongated olivine crystallites containing up to 14 wt% P2O5, amorphous material, and interstitial Cl-apatite crystals. The Si-rich silicate glass globules show a second population of Fe-rich silicate glass droplets, indicating they formed by silicate liquid immiscibility. Together with the presence of phosphoran olivine and quenched Cl-apatite, these textures suggest rapid cooling and quenching as a consequence of an impact event. Moreover, the enrichment of phosphorus in the silicate inclusion close to the metal host (phosphoran olivine and Cl-apatite) indicates that phosphorus re-partitioned from the metal into the silicate phase upon cooling. This probably also took place in pallasite meteorites that contain late-crystallizing phases rich in phosphorus. Accordingly, our findings suggest that oxidation of phosphorus might be a general process in core–mantle environments, bearing on our understanding of planetesimal evolution. Thus, the Netschaëvo sample serves as a natural planetesimal core–mantle boundary experiment and based on our temperature estimates, the following sequence of events takes place: (i) precipitation of olivine (1400–1360 °C), (ii) re-partitioning of phosphorus from the metal into the silicate phase, and (iii) formation of immiscible melts (1230–1115 °C).SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Plasmodium

Malaria is the most important parasitic disease worldwide in terms of numbers of affected people and mortality. It is caused by parasites of the genus Plasmodium, which have a complex life cycle including insect vectors that are in the case of human malaria exclusively Anopheles mosquitoes. To date the genomes of several Plasmodium species have been sequenced. The overall genome organization is rather conserved, but highly divers species-specific gene families have been identified as well. The different life cycle stages exhibit a very variable morphology reflecting their respective needs. The change in cell shape during development is genetically inherited, but epigenetic factors also appear to play an important role. In the vertebrate host cell invasion and egress are crucial steps for the survival of the parasite and have evolved to highly orchestrated events, and some molecular details have been deciphered to date. Invasion occurs by invagination of the host cell membrane, and the parasite finally resides in a parasitophorous vacuole. From there it controls the behavior of its host cell by secretion of proteins into the host cell cytoplasm and to its surface. Exposed parasite proteins at the surface of an infected red blood cell allow cytoadherence and are responsible for the pathogenicity of a Plasmodium infection. Egress is a two-step process initiated by the rupture of the parasitophorous vacuole membrane and followed by disintegration of the host cell membrane that involves the activation of proteases, kinases, and membrane lytic enzymes. Recent discoveries revealed completely new parasite strategies to switch from asexual to sexual development during the blood stage and to avoid elimination by cytosolic immune responses of host cells during infection of hepatocytes