2,880 research outputs found
GRBs from unstable Poynting dominated outflows
Poynting flux driven outflows from magnetized rotators are a plausible
explanation for gamma-ray burst engines. We suggest a new possibility for how
such outflows might transfer energy into radiating particles. We argue that the
Poynting flux drives non-linearly unstable large amplitude electromagnetic
waves (LAEMW) which ``break'' at radii cm where the MHD
approximation becomes inapplicable. In the ``foaming'' (relativisticly
reconnecting) regions formed during the wave breaks the random electric fields
stochastically accelerate particles to ultrarelativistic energies which then
radiate in turbulent electromagnetic fields. The typical energy of the emitted
photons is a fraction of the fundamental Compton energy with plus additional boosting due to the bulk motion
of the medium. The emission properties are similar to synchrotron radiation,
with a typical cooling time sec. During the wave break, the
plasma is also bulk accelerated in the outward radial direction and at larger
radii can produce afterglows due to the interactions with external medium. The
near equipartition fields required by afterglow models maybe due to magnetic
field regeneration in the outflowing plasma (similarly to the field generation
by LAEMW of laser-plasma interactions) and mixing with the upstream plasma.Comment: 15 pages, 1 figur
Practical issues in catalytic and hydrothermal biomass conversion: concentration effects on reaction pathways
Converting biomass to biofuels and chemicals calls for practical and simple processes, since it must compete economically with both burning and anaerobic bacterial digestion. Here we employ concentrated glucose solutions as a biomass model compound, using a pressure-controlled batch reactor setup for hydrothermal and catalytic upgrading. We examine the hydrothermal, acid-catalysed and base-catalysed reactions of concentrated glucose giving gases, tar (biofuels), and char products, and show that working at practical (i.e., high) feed concentrations has a strong effect on the reaction pathways
Understanding catalytic biomass conversion through data mining
Catalytic conversion of biomass is a key challenge that we chemists face in the twenty-first century. Worldwide, research is conducted into obtaining bulk chemicals, polymers and fuels. Our project centres on glucose valorisation via furfural derivatives using catalytic hydrogenation. We present here new results for a set of 48 bimetallic catalysts supported on silica, and demonstrate the application of data mining tools to identify major trends in the data. These results are combined with a full factorial data set for the hydrogenation of 5-ethoxymethylfurfural over alumina-supported transition metal catalysts. All the catalysts in the combined datasets were synthesized and tested for performance under identical conditions. This, combined with the fact that no combinations of metals were left out, enables the use of advanced data mining tools. The paper describes the data and highlights the relevant trends from a chemist’s viewpoint
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