Evolution and ecology of influenza A viruses.

Cosmochemistry of the rare earth elements: meteorite studies.

▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...

/pdf/luminous-infrared-galaxies-zoi3y3hutv.pdf

Luminous infrared galaxies

We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending on the interstellar environment through which the light travels. As shown by Cardelli, Clayton, and Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, RV. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for RV and bC, the C abundance in very small grains. We also find size distributions for the line of sight to HD 210121 and for sight lines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter and present model extinction curves extending beyond the Lyman limit.

https://iopscience.iop.org/article/10.1086/318651/pdf

Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

A variety of pigmented microorganisms have been identified in the red, yellow, blue and black rain that fell over Sri Lanka in December 2012 and January 2013. There is tentative evidence for the presence of similar organisms, including diatoms, in meteorites falling over the same time period. These microorganisms are likely to have served as nuclei for the condensation of rain drops.

Microorganisms in the Coloured Rain of Sri Lanka

Refractory grains of graphite and silicates ejected from cool giant stars acquire mantles of organic polymers typified by polyoxymethyline in interstellar clouds. Infrared emission from theTrapezium nebula is consistent with the occurrence of such polymers.

Formaldehyde Polymers in Interstellar Space

It is argued that the infrared emission including 10 and 18/~ features observed in recent con'Lets is unlikely to be due to silicates. The vaporization temperature of the emitting material 500 K is consistent with emission by crystalline polyformaldehyde, There )has been a significant advance in recent years of our knowledge of the chemical composition of the volatile ('icy') component of comets, which is ultimately respon- sible for the gaseous emission in the coma and plasma tail. At least in a majority of comets this component seems to be dominated by H20 ice, with other species trapped as impurities in the H20 lattice to form clathrates (Delsemme, 1973; Mendis and Ip,

Composition of cometary dust

Grains ejected from stars at velocities of ∼ 107cm s−1 and/or grains accelerated by the pressure of starlight in the intercloud medium to velocities in the range 2 × 106 –107 cm s−1 are slowed to velocities of about 2 × 105 cm s−1 in a typical interstellar cloud. The interaction of fast grains with gas atoms as they are slowed in clouds could provide (a) the dominant heat source for interstellar clouds; (b) sites for molecule formation; and (c) a mechanism of providing a pressure balance between clouds and the intercloud medium.

Effects of Suprathermal Grains

Earlier studies of the Tissint Martian meteorite identified the presence of a number of 5-50μm carbonaceous spherical structures. SEM and EDS elemental spectra for 11 selected structures confirmed that they comprise of a carbonaceous outer coating with a inner core of FeS 2 (pyrite) and are characterised as immiscible globules with curved boundaries. Here we report on the results of Raman spectroscopic studies that unambiguously confirm the mantle as comprising of ‘disordered carbonaceous material’. R1 = I D /I G against Γ D (cm -1 ) band parameter plots of the carbonaceous coatings imply a complex precursor carbon inventory comparable to the precursor carbon component of materials of known biotic source (plants, algae, fungi, crustaceans, prokaryotes). Correlation between peak metamorphic temperatures and Raman D-band (Γ D ) parameters further indicate the carbonaceous component was subjected to a peak temperature of ~250 O C suggesting a possible link with the hydrothermal precipitation processes responsible for the formation of similar globules observed in hydrothermal calcite veins in central Ireland. Ω G (cm -1 ), Γ G (cm -1 ), Ω D (cm -1 ) and Γ D (cm -1 ) parameters further imply a level of crystallinity and disorder of the carbon component consistent with carbonaceous material recovered from a variety of non-terrestrial sources. Cl, N, O and S to C elemental ratios are typical of high volatility bituminous coals and distinctly higher than equivalent graphite standards.

N. C. Wickramasinghe

Papers

Microorganisms in the Coloured Rain of Sri Lanka

Formaldehyde Polymers in Interstellar Space

Composition of cometary dust

Effects of Suprathermal Grains

Chemical and structural composition of organic carbonaceous structures in Tissint: evidence for a biogenetic origin