226,980 research outputs found
Engineering a Conformant Probabilistic Planner
We present a partial-order, conformant, probabilistic planner, Probapop which
competed in the blind track of the Probabilistic Planning Competition in IPC-4.
We explain how we adapt distance based heuristics for use with probabilistic
domains. Probapop also incorporates heuristics based on probability of success.
We explain the successes and difficulties encountered during the design and
implementation of Probapop
An example of optimal field cut in lattice gauge perturbation theory
We discuss the weak coupling expansion of a one plaquette SU(2) lattice gauge
theory. We show that the conventional perturbative series for the partition
function has a zero radius of convergence and is asymptotic. The average
plaquette is discontinuous at g^2=0. However, the fact that SU(2) is compact
provides a perturbative sum that converges toward the correct answer for
positive g^2. This alternate methods amounts to introducing a specific coupling
dependent field cut, that turns the coefficients into g-dependent quantities.
Generalizing to an arbitrary field cut, we obtain a regular power series with a
finite radius of convergence. At any order in the modified perturbative
procedure, and for a given coupling, it is possible to find at least one (and
sometimes two) values of the field cut that provide the exact answer. This
optimal field cut can be determined approximately using the strong coupling
expansion. This allows us to interpolate accurately between the weak and strong
coupling regions. We discuss the extension of the method to lattice gauge
theory on a D-dimensional cubic lattice.Comment: 9 pages, 11 figs., uses revtex4, modified presentatio
Towards First-principles Electrochemistry
Chemisorbed molecules at a fuel cell electrode are a very sensitive probe of
the surrounding electrochemical environment, and one that can be accurately
monitored with different spectroscopic techniques. We develop a comprehensive
electrochemical model to study molecular chemisorption at either constant
charge or fixed applied voltage, and calculate from first principles the
voltage dependence of vibrational frequencies -- the vibrational Stark effect
-- for CO adsorbed on close-packed platinum electrodes. The predicted
vibrational Stark slopes are found to be in very good agreement with
experimental electrochemical spectroscopy data, thereby resolving previous
controversies in the quantitative interpretation of in-situ experiments and
elucidating the relation between canonical and grand-canonicaldescriptions of
vibrational surface phenomena.Comment: 10 pages, 2 figure
Ratcheting Heat Flux against a Thermal Bias
Merely rocking the temperature in one heat bath can direct a steady heat flux
from cold to hot against a non-zero thermal bias in stylized nonlinear lattice
junctions that are sandwiched between two heat baths. Likewise, for an average
zero-temperature difference between the two contacts a net, ratchet-like heat
flux emerges. Computer simulations show that this very heat flux can be
controlled and reversed by suitably tailoring the frequency ( 100
MHz) of the alternating temperature field.Comment: 5 pages, 6 figure
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