21 research outputs found
Galactic Effects on Habitability
The galactic environment has been suspected to influence planetary
habitability in many ways. Very metal-poor regions of the Galaxy, or those
largely devoid of atoms more massive than H and He, are thought to be unable to
form habitable planets. Moreover, if such planets do form, the young system is
subjected to close stellar passages while it resides in its stellar birth
cluster. Various potential hazards remain after clusters disperse. For
instance, central galactic regions may present risks to habitability via nearby
supernovae, gamma ray bursts (GRBs), and frequent comet showers. In addition,
planets residing within very wide binary star systems are affected by the
Galaxy, as local gravitational perturbations from the Galaxy can increase the
binary's eccentricity until it destabilizes the planets it hosts. Here we
review the most recent work on the main galactic influences over planetary
habitability. Although there must be some metallicity limit below which rocky
planets cannot form, recent exoplanet surveys show that they form around stars
with a very large range of metallicities. Once formed, the probability of star
clusters destabilizing planetary systems only becomes high for rare, extremely
long-lived clusters. Regarding threats to habitability from supernovae, GRBs,
and comet showers, many recent studies suggest that their hazards are more
limited than originally thought. Finally, denser regions of the Galaxy enhance
the threat that very wide binary companions pose to planetary habitability, but
the probability that a very wide binary star disrupts habitability will always
be substantially below 100% for any environment. While some Milky Way regions
must be more hospitable to habitable planets than others, it is difficult to
state that habitable planets are confined to any well-defined region of the
Galaxy or that any other particular region of the Galaxy is uninhabitable.Comment: Invited review chapter, accepted for publication in the "Handbook of
Exoplanets"; 19 pages; 2 figure
Notes for genera: basal clades of Fungi (including Aphelidiomycota, Basidiobolomycota, Blastocladiomycota, Calcarisporiellomycota, Caulochytriomycota, Chytridiomycota, Entomophthoromycota, Glomeromycota, Kickxellomycota, Monoblepharomycota, Mortierellomycota, Mucoromycota, Neocallimastigomycota, Olpidiomycota, Rozellomycota and Zoopagomycota)
Compared to the higher fungi (Dikarya), taxonomic and evolutionary studies on the basal clades of fungi are fewer in number. Thus, the generic boundaries and higher ranks in the basal clades of fungi are poorly known. Recent DNA based taxonomic studies have provided reliable and accurate information. It is therefore necessary to compile all available information since basal clades genera lack updated checklists or outlines. Recently, Tedersoo et al. (MycoKeys 13:1--20, 2016) accepted Aphelidiomycota and Rozellomycota in Fungal clade. Thus, we regard both these phyla as members in Kingdom Fungi. We accept 16 phyla in basal clades viz. Aphelidiomycota, Basidiobolomycota, Blastocladiomycota, Calcarisporiellomycota, Caulochytriomycota, Chytridiomycota, Entomophthoromycota, Glomeromycota, Kickxellomycota, Monoblepharomycota, Mortierellomycota, Mucoromycota, Neocallimastigomycota, Olpidiomycota, Rozellomycota and Zoopagomycota. Thus, 611 genera in 153 families, 43 orders and 18 classes are provided with details of classification, synonyms, life modes, distribution, recent literature and genomic data. Moreover, Catenariaceae Couch is proposed to be conserved, Cladochytriales Mozl.-Standr. is emended and the family Nephridiophagaceae is introduced
Piezonuclear fission reactions: evidences from microchemical analysis, neutron emission, and geological transformation
Neutron emission measurements, by means of He3 devices and bubble detectors, were performed during three different kinds of compression tests on brittle rocks: (1) under monotonic displacement control, (2) under cyclic loading, and (3) by ultrasonic vibration. The material used for the tests was Luserna Stone. Since the analyzed material contains iron, our conjecture is that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. This hypothesis is confirmed by the direct evidence of energy dispersive X-ray spectroscopy tests conducted on Luserna Stone specimens. It is also interesting to emphasize that the anomalous chemical balances of the major events that have affected the geomechanical and geochemical evolution of the Earth's crust should be considered as an indirect evidence of the piezonuclear fission reactions considered abov