94 research outputs found
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Rf-plasma synthesis of nanosize silicon carbide and nitride. Final report
A pulsed rf plasma technique is capable of generating ceramic particles of 10 manometer dimension. Experiments using silane/ammonia and trimethylchlorosilane/hydrogen gas mixtures show that both silicon nitride and silicon carbide powders can be synthesized with control of the average particle diameter from 7 to 200 nm. Large size dispersion and much agglomeration appear characteristic of the method, in contrast to results reported by another research group. The as produced powders have a high hydrogen content and are air and moisture sensitive. Post-plasma treatment in a controlled atmosphere at elevated temperature (800{degrees}C) eliminates the hydrogen and stabilizes the powder with respect to oxidation or hydrolysis
Size Doesn't Matter: Towards a More Inclusive Philosophy of Biology
notes: As the primary author, O’Malley drafted the paper, and gathered and analysed data (scientific papers and talks). Conceptual analysis was conducted by both authors.publication-status: Publishedtypes: ArticlePhilosophers of biology, along with everyone else, generally perceive life to fall into two broad categories, the microbes and macrobes, and then pay most of their attention to the latter. ‘Macrobe’ is the word we propose for larger life forms, and we use it as part of an argument for microbial equality. We suggest that taking more notice of microbes – the dominant life form on the planet, both now and throughout evolutionary history – will transform some of the philosophy of biology’s standard ideas on ontology, evolution, taxonomy and biodiversity. We set out a number of recent developments in microbiology – including biofilm formation, chemotaxis, quorum sensing and gene transfer – that highlight microbial capacities for cooperation and communication and break down conventional thinking that microbes are solely or primarily single-celled organisms. These insights also bring new perspectives to the levels of selection debate, as well as to discussions of the evolution and nature of multicellularity, and to neo-Darwinian understandings of evolutionary mechanisms. We show how these revisions lead to further complications for microbial classification and the philosophies of systematics and biodiversity. Incorporating microbial insights into the philosophy of biology will challenge many of its assumptions, but also give greater scope and depth to its investigations
Structural brain correlates of childhood inhibited temperament: an ENIGMA-Anxiety Mega-analysis
NWORubicon 019.201SG.022Pathways through Adolescenc
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DEVELOPMENT OF A SUPERSONIC ATOMIC OXYGEN NOZZLE EEAM SOURCE FOR CROSSED BEAM SCATTERING EXPERIMENTS
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Nanoparticle synthesis in pulsed low temperature discharges
Silicon nitride powders with an average size as low as 7 nm are synthesized in a pulsed radio frequency glow discharge. The as-synthesized silicon nitride powder from a silane/ammonia plasma has a high hydrogen content and is sensitive to oxidation in air. Post-plasma heating of the powder in a vacuum results in nitrogen loss, giving silicon-rich powder. In contrast, heat treatment at 800 C for 20 minutes in an ammonia atmosphere (200 Torr pressure) yields a hydrogen-free powder which is stable with respect to atmospheric oxidation. Several approaches to synthesizing silicon carbide nano-size powders are presented. Experiments using silane/hydrocarbon plasmas produce particles with a high hydrogen content as demonstrated by Fourier transform infrared analysis. The hydrogen is present as both CH and SiH functionality. These powders are extremely air-sensitive. A second approach uses a gas mixture of methyltrichlorosilane and hydrogen. The particles have a low hydrogen content and resist oxidation. Particle morphology of the silicon carbide is more spherical and there is less agglomeration than is observed in the silicon nitride powder
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CROSSED MOLECULAR BEAM STUDIES OF UN-IMOLECULAR REACTION DYNAMICS
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Synthesis of silicon nitride powders in pulsed RF plasmas
Nanometer size silicon nitride particles are synthesized using a pulsed radio frequency plasma technique. The plasma is modulated with a square-wave on/off cycle of varying period to control size and morphology and to deduce the growth kinetics. In situ laser light scattering and ex situ particle analysis are used to study the nucleation and growth. For SiH{sub 4}/Ar plasmas which nucleate silicon particles, an initial extremely rapid growth phase is followed by a slower growth rate, approaching the rate of thin film deposition on adjacent flat surfaces. In SiH{sub 4}/NH{sub 3} plasmas, silicon nitride particle size can be tightly controlled by adjusting the plasma-on time. The size dispersion of the particles is large and is consistent with a process of continual nucleation during the plasma-on period. The observed polydispersity differs dramatically from that reported from other laboratories
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Reaction mechanism of oxygen atoms with unsaturated hydrocarbons by the crossed molecular beams method
From a series of studies of the reaction of oxygen atoms with unsaturated hydrocarbons using the crossed molecular beam method, the dominant reaction mechanisms were found to be the simple substitution reactions with oxygen atoms replacing H, Cl, Br atom or alkyl groups. Complication due to secondary reaction was avoided by carrying out experiments under single collisions and observing primary products directly. Primary products were identified by measuring the angular and velocity distributions of products at all the mass numbers which could be detected by the mass spectrometer, and from comparison of these distributions, applying the requirement of energy and momentum conservation
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