1,565 research outputs found
A new type of photoionized code required for the new era of X-ray spectroscopy
With the advent of the present and future spatial X-ray missions, it becomes
crucial to model correctly the line spectrum of X-ray emitting media. We have
built a photoionization code, Titan, solving the transfer of a thousand lines
and of the continuum with the "Accelerated Lambda Iteration" method, which is
most reliable for line transfer. In all other photoionization codes the line
intensities are computed with the so-called "escape probability formalism",
used in its simplest approximation. In a previous paper (Dumont et al. 2003),
it was shown that this approximation leads to errors which can exceed one order
of magnitude in the case a Thomson thickness of the order of unity. We show
here that it also happens in the case of a Thomson thickness of 0.001 to 0.1.
The errors on the line fluxes and line ratios are of the order of 30% for a
column density of 10^{20} cm^{-2}, and a factor five for a column density of
10^{23} cm^{-2}, in conditions appropriate for Seyfert 2 and for the Warm
Absorber of Seyfert 1.Comment: 11 pages, 7 figures. accepted by A&
Assessing the environmental potential of carbon dioxide utilization: A graphical targeting approach
Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO2 is intrinsically difficult due to its low energetic state. Thus, a positive environmental effect of a CO2-consuming reaction cannot be taken for granted. In this work, we therefore present a graphical method to identify promising reaction schemes using CO2 as a feedstock. Reactant mixtures leading to minimal life-cycle greenhouse gas (GHG) emissions are determined. The optimal reaction schemes strongly depend on the reactantsâ global warming potential (GWP); in the case of CCU, the future GWP values of CO2 and H2 are particularly critical and subject to major uncertainty today. The graphical method therefore provides GWP targets for CO2 capture and H2 production technologies. The method is demonstrated for the production of methanol. Five optimal reaction schemes are identified depending on the GWP values of CO2 and H2. Thus, four threshold relations for the GWP of CO2 and H2 are derived showing directly under which conditions the utilization of CO2 as a feedstock is environmentally preferential
Alien Registration- Dumont, Marie A. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/29467/thumbnail.jp
Alien Registration- Dumont, Marie Anne (Auburn, Androscoggin County)
https://digitalmaine.com/alien_docs/31232/thumbnail.jp
Alien Registration- Dumont, Marie L. (Auburn, Androscoggin County)
https://digitalmaine.com/alien_docs/31233/thumbnail.jp
Systemes de numeration et fonctions fractales relatifs aux substitutions
AbstractLet A be a finite alphabet, Ï a substitution over A, (un)n Ï” N a fixed point for Ï, and for each a Ï” A, Æ(a) a real number. We establish, under some assumptions, an asymptotic formula concerning the sum SÆ (N) = ÎŁi â©œ N Æ(ui), N Ï” N. This result generalizes some previous results from Coquet or Brillhart, Erdös, and Morton. Moreover, relations with self-affine functions (in a sense which generalizes a definition from Kamae) are proved. The calculi leave over systems of representation of integers and real numbers
5âHydroxymethylfurfural derivative based thermoplastic elastomers synthesized via thiolâMichael addition reaction utilizing poly (lactic acid) as hard end blocks
5-Hydroxymethylfurfural derivative based thermoplastic elastomers (TPEs) are effciently synthesized via a two-step thiol-Michael addition reaction using polylactide (PLA) as the hard segments in a one-pot reaction under mild conditions. The first step involves the synthesis of prepolymers having thiolgroups as end groups. The macromolecular coupling reaction which occurred between the prepolymers and the PLA having acrylate-end groups is demonstrated via 1H NMR and GPC. Additionally, by varying the ratio of 1,3-propanedithiol and 2,5-furan diacrylate, TPEs with soft segments having different molecular weights are synthesized, and then characterized. The cyclic tensile tests demonstrate the elasticity of the synthesized TPEs. Furthermore, the DielsâAlder reaction is used to dynamically crosslink the soft segments in the TPEs, leading to the increased mechanical properties in terms of Young's modulus and tensile strength
Advances in polymer precursors and bioâbased polymers synthesized from 5âhydroxymethylfurfural
In recent years, considerable efforts have been made regarding the synthesis of renewable chemicals from natural resources. 5-hydroxymethylfurfural (HMF) is an interesting platform chemical which has been widely exploited due to its rich chemistry and potential availability. The versatility of HMF has been demonstrated in several areas such as fine chemicals, biofuel precursors and polymers. In particular, the potential to replace petroleum-based analogues in the preparation of polymers associated with high performance has been observed owing to the structural rigidity of furan rings. This review aims at critically discuss the current research studies related to the derivatives of HMF, alongside with the synthesis and characterization of (co-) polymers derived from HMF and its derivatives
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