Mesoporous amorphous silicate catalysts for biogas reforming

Diatoms are phototrophic single-celled microalgae encased in a cell wall (frustule) made of amorphous silicate. The frustule comprises two valves connected by a variable number of girdle bands, all exhibiting periodic micro/nanoporous structures. We studied the optical properties in water of girdle bands from the centric diatom Coscinodiscus granii , a frustule part that so far has received little attention by the scientific community. We show that valves and girdle bands exhibit different optical properties, as valves attenuate shorter wavelengths and girdle bands attenuate longer wavelengths of the visible light spectrum. Girdle bands show iridescent coloration in dependence of the light direction. Although the biological meaning of periodic nanoscale structures of frustules is still a matter of debate, the differences of valve and girdle band optical properties indicate that living diatoms are complex optical systems, where valves, girdles and pigments modulate light inside the cell.

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Thermal emission from the amorphous dust: An alternative possibility of the origin of the anomalous microwave emission

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz124 ◽

2019 ◽

Vol 72 (1) ◽

Cited By ~ 1

Author(s):

Masashi Nashimoto ◽

Makoto Hattori ◽

Ricardo Génova-Santos ◽

Frédérick Poidevin

Keyword(s):

Interstellar Dust ◽

Amorphous Materials ◽

Thermal Emission ◽

Far Infrared ◽

Alternative Interpretation ◽

Microwave Emission ◽

Spectral Energy ◽

Radiative Processes ◽

Resonance Emission ◽

Amorphous Silicate

Abstract Complete studies of the radiative processes of thermal emission from the amorphous dust from microwave through far-infrared wavebands are presented by taking into account, self-consistently for the first time, the standard two-level systems (TLS) model of amorphous materials. The observed spectral energy distributions (SEDs) for the Perseus molecular cloud (MC) and W 43 from microwave through far-infrared are fitted with the SEDs calculated with the TLS model of amorphous silicate. We have found that the model SEDs reproduce the observed properties of the anomalous microwave emission (AME) well. The present result suggests an alternative interpretation for the AME being carried by the resonance emission of the TLS of amorphous materials without introducing new species. Simultaneous fitting of the intensity and polarization SEDs for the Perseus MC and W 43 are also performed. The amorphous model reproduces the overall observed feature of the intensity and polarization SEDs of the Perseus MC and W 43. However, the model’s predicted polarization fraction of the AME is slightly higher than the QUIJOTE upper limits in several frequency bands. A possible improvement of our model to resolve this problem is proposed. Our model predicts that interstellar dust is amorphous materials with very different physical characteristics compared with terrestrial amorphous materials.

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Amorphous Silicate Building Block Origins by Transmission Electron Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927618010838 ◽

2018 ◽

Vol 24 (S1) ◽

pp. 2070-2071

Author(s):

Hope A. Ishii ◽

James Ciston ◽

John P. Bradley ◽

Karen Bustillo ◽

Peter Ercius

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Building Block ◽

Transmission Electron ◽

Amorphous Silicate

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Physical vapor deposition synthesis of amorphous silicate layers and nanostructures as cosmic dust analogs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201527222 ◽

2016 ◽

Vol 589 ◽

pp. A4 ◽

Cited By ~ 3

Author(s):

A. De Sio ◽

L. Tozzetti ◽

Ziyu Wu ◽

A. Marcelli ◽

M. Cestelli Guidi ◽

...

Keyword(s):

Vapor Deposition ◽

Physical Vapor Deposition ◽

Cosmic Dust ◽

Amorphous Silicate ◽

Silicate Layers

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The Composition of Dust in Stellar Ejecta

Symposium - International Astronomical Union ◽

10.1017/s0074180900125458 ◽

1989 ◽

Vol 135 ◽

pp. 455-466 ◽

Cited By ~ 2

Author(s):

D. C. B. Whittet

Keyword(s):

Amorphous Carbon ◽

Far Infrared ◽

Infrared Emission ◽

Major Goal ◽

Important Ingredient ◽

Future Studies ◽

Predominant Species ◽

Amorphous Silicate ◽

Circumstellar Shells ◽

A Minor

I review the observational evidence relevant to the composition of dust ejected from circumstellar shells. Emphasis is placed on those types of stars believed to be the principal sources of refractory stardust in the interstellar medium. In stars with normal abundances (O > C), the predominant species appears to be an amorphous silicate, characterised by smooth spectral features at 9.7 and 19μm, a far infrared emissivity close to unity, and a featureless ultraviolet extinction curve. Similarly, the characteristics of carbon stars (C > O) are consistent with the presence of amorphous carbon rather than graphite. Silicon carbide is a minor constituent of carbon-rich stardust and is therefore unlikely to be an important ingredient of interstellar grains. A major goal for future studies will be to establish the evolutionary link between amorphous carbon stardust and the carriers of the unidentified infrared emission features observed in planetary nebulae.

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