1,236 research outputs found
Electric discharge for treatment of trace contaminants
A radio frequency glow discharge reactor is described for removing trace oxidizable contaminants from an oxygen bearing atmosphere. The reaction chamber is defined by an inner metal electrode facing a dielectric backed by an outer conductive electrode. In one embodiment, a conductive liquid forms the conductor of an outer electrode and cools the dielectric. A resonator coupled to a variable radio frequency source generates the high voltages for creating a glow discharge in the chamber at a predetermined pressure whereby the trace contaminants are oxidized into a few simple non-toxic products that may be easily recovered. The corresponding process for removal of trace contaminants from an oxygen-bearing atmosphere with high efficiency independent of the concentration level is also disclosed
Inferring Chemical Reaction Patterns Using Rule Composition in Graph Grammars
Modeling molecules as undirected graphs and chemical reactions as graph
rewriting operations is a natural and convenient approach tom odeling
chemistry. Graph grammar rules are most naturally employed to model elementary
reactions like merging, splitting, and isomerisation of molecules. It is often
convenient, in particular in the analysis of larger systems, to summarize
several subsequent reactions into a single composite chemical reaction. We use
a generic approach for composing graph grammar rules to define a chemically
useful rule compositions. We iteratively apply these rule compositions to
elementary transformations in order to automatically infer complex
transformation patterns. This is useful for instance to understand the net
effect of complex catalytic cycles such as the Formose reaction. The
automatically inferred graph grammar rule is a generic representative that also
covers the overall reaction pattern of the Formose cycle, namely two carbonyl
groups that can react with a bound glycolaldehyde to a second glycolaldehyde.
Rule composition also can be used to study polymerization reactions as well as
more complicated iterative reaction schemes. Terpenes and the polyketides, for
instance, form two naturally occurring classes of compounds of utmost
pharmaceutical interest that can be understood as "generalized polymers"
consisting of five-carbon (isoprene) and two-carbon units, respectively
Generic Strategies for Chemical Space Exploration
Computational approaches to exploring "chemical universes", i.e., very large
sets, potentially infinite sets of compounds that can be constructed by a
prescribed collection of reaction mechanisms, in practice suffer from a
combinatorial explosion. It quickly becomes impossible to test, for all pairs
of compounds in a rapidly growing network, whether they can react with each
other. More sophisticated and efficient strategies are therefore required to
construct very large chemical reaction networks.
Undirected labeled graphs and graph rewriting are natural models of chemical
compounds and chemical reactions. Borrowing the idea of partial evaluation from
functional programming, we introduce partial applications of rewrite rules.
Binding substrate to rules increases the number of rules but drastically prunes
the substrate sets to which it might match, resulting in dramatically reduced
resource requirements. At the same time, exploration strategies can be guided,
e.g. based on restrictions on the product molecules to avoid the explicit
enumeration of very unlikely compounds. To this end we introduce here a generic
framework for the specification of exploration strategies in graph-rewriting
systems. Using key examples of complex chemical networks from sugar chemistry
and the realm of metabolic networks we demonstrate the feasibility of a
high-level strategy framework.
The ideas presented here can not only be used for a strategy-based chemical
space exploration that has close correspondence of experimental results, but
are much more general. In particular, the framework can be used to emulate
higher-level transformation models such as illustrated in a small puzzle game
Embedding the Reissner-Nordstrom spacetime in Euclidean and Minkowski spaces
We examine embedding diagrams of hypersurfaces in the Reissner-Nordstrom
black hole spacetime. These embedding diagrams serve as useful tools to
visualize the geometry of the hypersurfaces and of the whole spacetime in
general.Comment: 13 pages, 10 figure
The three-quark static potential in perturbation theory
We study the three-quark static potential in perturbation theory in QCD. A
complete next-to-leading order calculation is performed in the singlet, octets
and decuplet channels and the potential exponentiation is demonstrated. The
mixing of the octet representations is calculated. At next-to-next-to-leading
order, the subset of diagrams producing three-body forces is identified in
Coulomb gauge and its contribution to the potential calculated. Combining it
with the contribution of the two-body forces, which may be extracted from the
quark-antiquark static potential, we obtain the complete
next-to-next-to-leading order three-quark static potential in the
colour-singlet channel.Comment: 36 pages, 11 figures, version published in Phys.Rev.
Computational Chemistry with RNA Secondary Structures
The secondary structure for nucleic acids provides a level of description that is both abstract enough to allow for efficient algorithms and realistic enough to provide a good approximate to the thermodynamic and kinetics properties of RNA structure formation. The secondary structure model has furthermore been successful in explaining salient features of RNA evolution in nature and in the test tube. In this contribution we review the computational chemistry of RNA secondary structures using a simplified algorithmic approach for explanation
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