A POORLY GRAPHITISED CARBON CONTAMINANT IN STUDIES OF EXTRATERRESTRIAL MATERIALS

Poorly-graphitised carbon particles are formed during manufacture of sample substrates (holey carbon films) for Analytical Electron Microscopy studies of small particles. The particles form during heat treatment of cellulose acetobutyrate at about 975 °C and 1050 °C. In AEM studies of fine-grained carbonaceous extraterrestrial materials, these particles are easily recognised.     

Imposing Age and Spatial Structures on Inadequate Migration‐Flow Datasets*

With the elimination of the long‐form questionnaire from future decennial censuses and its replacement by a much smaller continuous monthly sampling survey (the American Community Survey), students of territorial mobility may find it necessary to deal with inadequate, missing, or inaccurate sample data on migration by adopting an approach that “improves” such data using information from different geographical areas, time periods, and data sources. We develop such an approach in this article and illustrate it with interregional migration flow data reported by the U.S. decennial censuses of 1980 and 1990 and by the 1985 Current Population Survey.     

Understanding the mechanisms of formation of nanophase compounds from Stardust: Combined experimental and observational approach

Abstract– We have experimentally produced nanophase sulfide compounds and magnetite embedded in Si‐rich amorphous materials by flash‐cooling of a gas stream. Similar assemblages are ubiquitous, and often dominant components of samples of impact‐processed silica aerogel tiles and submicron grains from comet 81P/Wild 2 were retrieved by NASA’s Stardust mission. Although the texture and compositions of nanosulfide compounds have been reproduced experimentally, the mechanisms of formation of these minerals and their relationship with the surrounding amorphous materials have not been established. In this study, we present evidence that both of these materials may not only be produced through cooling of a superheated liquid but they may have also been formed simultaneously by flash‐cooling and subsequent deposition of a gas dominated by Fe‐S‐SiO‐O₂. In a dust generator at the Goddard Space Flight Center, samples are produced by direct gas‐phase condensation from gaseous precursors followed by deposition, which effectively isolates the effects of gas‐phase reactions from the effects of melting and condensation. High‐resolution transmission electron microscopy images and energy‐dispersive spectroscopy analysis show that these experiments replicate key features of materials from type B and type C Stardust tracks, including textures, distribution of inclusions, nanophase size, and compositional diversity. We argue that gas‐phase reactions may have played a significant role in the capture environment for nanophase materials. Our results are consistent with a potential progenitor assemblage of micron and submicron‐sized sulfides and submicron silica‐bearing phases, which are commonly observed in chondritic interplanetary dust particles and in the matrices of the most pristine chondritic meteorites.     

CM-like interplanetary dust particles in lower stratosphere during 1989 October and 1991 June/July

Abstract— The stratospheric interplanetary dust particles L2005T12 and L2011O3 are linked to CM chondrite matrix. Particle L2005T12 is dominated by tabular grains of partially dehydrated greenalite-rich serpentine. Its amorphous matrix contains abundant smectite nanocrystals and annular Fe, Ni, S units. A uniquely stratified (partial) maghémite rim occurs only on S-rich parts of the matrix. Formation of this rim and Mg depletions in the matrix occurred during atmospheric entry heating of this particle. Particle L2011O3 has large iron sulfide and magnesiowüstite grains in an amorphous low-Al, ferromagnesiosilica matrix. Hydrous crystallisation of this matrix produced ultrafine-grained smectites and disseminated iron sulfides. Atmospheric entry heating of both particles is indicated by the partial iron oxide rim, vesicular sulfides, and the scatter of matrix compositions due to loss of Mg. While many uncertainties remain, the high incidence of chondritic rough particles, which include an unknown amount of CM-like particles, in the lower stratosphere during 1984, 1989, and 1991 suggests annual variations in their abundances. The timing of lower stratospheric dust samplings is critical to collect these particles.     

Are crystalline C-(H-O-N) carbons the elusive meteoritic carbynes?

Abstract I present an internally consistent reinterpretation of carbyne diffraction data making a few plausible assumptions. The results support that carbynes could be crystalline, randomly interstratified (or mixed-layered) carbons with variable C/(C+H+O+N) ratios rather than thermodynamically stable carbon allotropes. The metastable carbynes are likely the result of incomplete, kinetically-inhibited, low-temperature pyrolysis of precursor material. A renewed interest in meteoritic carbynes should seek to combine light-element chemistry and crystallography of these elusive carbons.     

The ultrafine mineralogy of a molten interplanetary dust particle as an example of the quench regime of atmospheric entry heating

Abstract— Melting and degassing of interplanetary dust particle L2005B22 at ～1200 °C was due to flash heating during atmospheric entry. Preservation of the porous particle texture supports rapid quenching from the peak heating temperature whereby olivine and pyroxene nanocrystals (3 nm-26 nm) show partial devitrification of the quenched melt at T ? 450 °C–740 °C. The implied ultrahigh cooling rates are calculated at ～105 °C/h–106 °C/h, which is consistent with quench rates inferred from the temperature-time profiles based on atmospheric entry heating models. A vesicular rim on a nonstoichiometric relic forsterite grain in this particle represents either evaporative magnesium loss during flash heating or thermally annealed ion implantation texture.     

Tin in a chondritic interplanetary dust particle

Abstract— Submicron platey Sn-rich grains are present in chondritic porous interplanetary dust particle (IDP) W7029^*A and it is the second occurrence of a tin mineral in a stratospheric micrometeorite. Selected Area Electron Diffraction data for the Snrich grains match with Sn₂O₃ and Sn₃O₄. The oxide(s) may have formed in the solar nebula when tin metal catalytically supported reduction of CO or during flash heating on atmospheric entry of the IDP. The presence of tin is consistent with enrichments for other volatile trace elements in chondritic IDPs and may signal an emerging trend towards non-chondritic volatile element abundances in chondritic IDPs. The observation confirms small-scale mineralogical heterogeneity in fine-grained chondritic porous interplanetary dust.     

A proposal for a new scenario framework to support research and assessment in different climate research communities

In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities.