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...

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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

An excess red emission of interstellar dust observed over the waveband 5000-8000A is well fitted in terms of photoluminescence of biologically derived chromophores. The redness of the class of Edgeworth-Kuiper belt objects and of areas of the Martian surface may have a similar explanation.

Evidence of photoluminescence of biomaterial in space

We report the discovery for the first time of diatom frustules in a carbonaceous meteorite that fell in the North Central Province of Sri Lanka on 29 December 2012. Contamination is excluded by the circumstance that the elemental abundances within the structures match closely with those of the surrounding matrix. There is also evidence of structures morphologically similar to red rain cells that may have contributed to the episode of red rain that followed within days of the meteorite fall. The new data on fossil diatoms provide strong evidence to support the theory of cometary panspermia.

Fossil diatoms in a new carbonaceous meteorite

Small dielectric ice particles of radius ~0.25 Μm, which are known to be present in the mesophere, scatter a fraction of incident sunlight in backward directions that do not reach the Earth. This back-scattered fraction is rigorously calculated using Mie theory for a uniform distribution of particles distributed over a sunlit hemisphere. Such calculations provide necessary information for estimating equilibrium surface temperatures of the Earth under different conditions.

Back-scattering of sunlight by ice grains in the mesosphere

Nanometre-sized microdiamonds of the type recently discovered in meteorites could make up a significant fraction of interstellar carbon, and thus explain the observed excess of interstellar extinction at ultraviolet wavelengths.

Microdiamonds and the Ultraviolet Extinction of Starlight

Extinction and scattering efficiencies are calculated for spherically stratified graphite spheres using formulae which are valid in the small particle limit The resulting extinction curve for this model is shown to peak at an ultraviolet wavelengthλ
-1=48−5μ
-1 close to that for the case of the less probable plane stratified model of a graphite sphere The albedo in the present model is higher than that calculated for the plane stratified case by a factor 15–2 in the far ultraviolet Extinction curves are also obtained for the case of a dielectric sphere surrounded by a thin graphite film, and it is shown that there now is an extinction minimum atλ
-1≃46μ
-1

N. C. Wickramasinghe

Papers

Evidence of photoluminescence of biomaterial in space

Fossil diatoms in a new carbonaceous meteorite

Back-scattering of sunlight by ice grains in the mesosphere

Microdiamonds and the Ultraviolet Extinction of Starlight

The Optics of Spherically Stratified Graphite Grains