29 research outputs found
Tree Automata with Global Constraints for Infinite Trees
We study an extension of tree automata on infinite trees with global equality and disequality constraints. These constraints can enforce that all subtrees for which in the accepting run a state q is reached (at the root of that subtree) are identical, or that these trees differ from the subtrees at which a state q\u27 is reached. We consider the closure properties of this model and its decision problems. While the emptiness problem for the general model remains open, we show the decidability of the emptiness problem for the case that the given automaton only uses equality constraints
Sketch-based interaction and modeling: where do we stand?
Sketching is a natural and intuitive communication tool used for expressing concepts or ideas which are difficult to communicate through text or speech alone. Sketching is therefore used for a variety of purposes, from the expression of ideas on two-dimensional (2D) physical media, to object creation, manipulation, or deformation in three-dimensional (3D) immersive environments. This variety in sketching activities brings about a range of technologies which, while having similar scope, namely that of recording and interpreting the sketch gesture to effect some interaction, adopt different interpretation approaches according to the environment in which the sketch is drawn. In fields such as product design, sketches are drawn at various stages of the design process, and therefore, designers would benefit from sketch interpretation technologies which support these differing interactions. However, research typically focuses on one aspect of sketch interpretation and modeling such that literature on available technologies is fragmented and dispersed. In this paper, we bring together the relevant literature describing technologies which can support the product design industry, namely technologies which support the interpretation of sketches drawn on 2D media, sketch-based search interactions, as well as sketch gestures drawn in 3D media. This paper, therefore, gives a holistic view of the algorithmic support that can be provided in the design process. In so doing, we highlight the research gaps and future research directions required to provide full sketch-based interaction support
Improved Product-Per-Glucose Yields in P450-Dependent Propane Biotransformations Using Engineered Escherichia coli
P450-dependent biotransformations in Escherichia
coli are attractive for the selective oxidation of organic
molecules using mild and sustainable procedures. The overall
efficiency of these processes, however, relies on how
effectively the NAD(P)H cofactors derived from oxidation
of the carbon source are utilized inside the cell to support the
heterologous P450-catalyzed reaction. In this work, we
investigate the use of metabolic and protein engineering
to enhance the product-per-glucose yield (Y_(PPG)) in wholecell
reactions involving a proficient NADPH-dependent
P450 propane monooxygenase prepared by directed evolution
[P450_(PMO)R2; Fasan et al. (2007); Angew Chem Int Ed
46:8414–8418]. Our studies revealed that the metabolism of
E. coli (W3110) is able to support only a modest propanol:
glucose molar ratio (Y_(PPG)~0.5) under aerobic, nongrowing
conditions. By altering key processes involved in
NAD(P)H metabolism of the host, considerable improvements
of this ratio could be achieved. A metabolically
engineered E. coli strain featuring partial inactivation of
the endogenous respiratory chain (Δndh) combined with
removal of two fermentation pathways (ΔadhE, Δldh) provided
the highest YPPG (1.71) among the strains investigated,
enabling a 230% more efficient utilization of the energy
source (glucose) in the propane biotransformation compared
to the native E. coli strain. Using an engineered
P450_(PMO)R2 variant which can utilize NADPH and NADH
with equal efficiency, we also established that dual cofactor specificity of the P450 enzyme can provide an appreciable improvement in Y_(PPG). Kinetic analyses suggest, however,
that much more favorable parameters (K_M, k_(cat)) for the
NADH-driven reaction are required to effectively compete
with the host’s endogenous NADH-utilizing enzymes. Overall,
the metabolic/protein engineering strategies described
here can be of general value for improving the performance
of NAD(P)H-dependent whole-cell biotransformations in
E. coli