44,089 research outputs found
Heuristic Refinement Method for the Derivation of Protein Solution Structures: Validation on Cytochrome B562
A method is described for determining the family of protein structures compatible with solution data obtained primarily from nuclear magnetic resonance (NMR) spectroscopy. Starting with all possible conformations, the method systematically excludes conformations until the remaining structures are only those compatible with the data. The apparent computational intractability of this approach is reduced by assembling the protein in pieces, by considering the protein at several levels of abstraction, by utilizing constraint satisfaction methods to consider only a few atoms at a time, and by utilizing artificial intelligence methods of heuristic control to decide which actions will exclude the most conformations. Example results are presented for simulated NMR data from the known crystal structure of cytochrome b562 (103 residues). For 10 sample backbones an average root-mean-square deviation from the crystal of 4.1 A was found for all alpha-carbon atoms and 2.8 A for helix alpha-carbons alone. The 10 backbones define the family of all structures compatible with the data and provide nearly correct starting structures for adjustment by any of the current structure determination methods
Physical problem solving: Joint planning with symbolic, geometric, and dynamic constraints
In this paper, we present a new task that investigates how people interact
with and make judgments about towers of blocks. In Experiment~1, participants
in the lab solved a series of problems in which they had to re-configure three
blocks from an initial to a final configuration. We recorded whether they used
one hand or two hands to do so. In Experiment~2, we asked participants online
to judge whether they think the person in the lab used one or two hands. The
results revealed a close correspondence between participants' actions in the
lab, and the mental simulations of participants online. To explain
participants' actions and mental simulations, we develop a model that plans
over a symbolic representation of the situation, executes the plan using a
geometric solver, and checks the plan's feasibility by taking into account the
physical constraints of the scene. Our model explains participants' actions and
judgments to a high degree of quantitative accuracy
Extended quantum portrait of MGD black holes and information entropy
The extended minimal geometric deformation (EMGD) is employed on the fluid
membrane paradigm, to describe compact stellar objects as Bose--Einstein
condensates (BEC) consisting of gravitons. The black hole quantum portrait,
besides deriving a preciser phenomenological bound for the fluid brane tension,
is then scrutinized from the point of view of the configurational entropy. It
yields a range for the critical density of the EMGD BEC, whose configurational
entropy has global minima suggesting the configurational stability of the EMGD
BEC.Comment: 9 pages, 7 figures, matches the published versio
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