4,679 research outputs found
Learning and adaptation in physical agents
Learning and adaptation is fundamental for autonomous agents that operate in a physical world and not a computer network. The paper is providing a general framework of skills learning within behaviour logic framework of agents that communicate, sense and act in the physical world. It is advocated that playfulness can be important in learning and to improving skills of agents
Diffusion Kinetics in Radiation Chemistry. II. One-Radical-One-Solute Model; Calculations
The general diffusionâkinetic equations are applied to a oneâradicalâoneâsolute model of the radiolysis of dilute aqueous solutions. The validity of the prescribed diffusion approximation is examined. Results of calculations of the effect on the molecular and radical yields of the following parameters are given: solute concentration, solute depletion, shape of initial radical distribution, radical density, diffusion coefficients, and rate constants. Conditions under which a straight track of equal and equidistant spherical spurs can be replaced by either isolated spherical spurs or an axially homogeneous cylindrical track are examined
Nonmolecular nature of nitric-oxide-inhibited thermal decomposition of n-butane
The thermal decomposition of most organic molecules is generally accepted to occur at least in part via a free radical chain process. Since Hinshelwood and Staveley (1) discovered that small additions of nitric oxide reduced the rate of thermal decomposition, there has been much controversy (2) concerning the nature of the âresidualâ reaction remaining after further additions of inhibitor produce no further decrease in rate. Jach, Stubbs, and Hinshelwood (3) have shown this limiting rate to be independent of the inhibitor used and attribute this residual reaction to a nonchain molecular process in which the parent molecule breaks up, in a single step, into stable products
Quantum Mechanics of the H+H2 Reaction: Exact Scattering Probabilities for Collinear Collisions
The H + H2 reaction is very important in theoretical chemical dynamics (1-4). A model that is often used to study this reaction is to restrict the atoms to lie on a nonrotating line throughout the collision and to consider that the system is electronically adiabatic, i.e., it remains the lowest electronic state throughout the collision. This reduces the problem to scattering of three particles on a potential energy surface which is a function of two linearly independent coordinates. This model has been studied classically (5-8), and Mortensen and Pitzer (9) have calculated exact quantum mechanical reaction probabilities at five relative translational energies E0. In this Communication, we present some results of our more extensive exact calculations on this model of the H + H2 reaction and show their consequences for the validity of approximate theories of chemical reactions. For the cases considered here, the assumption of electronic adiabaticity causes very little error (10)
Fractional spins and static correlation error in density functional theory
Electronic states with fractional spins arise in systems with large static
correlation (strongly correlated systems). Such fractional-spin states are
shown to be ensembles of degenerate ground states with normal spins. It is
proven here that the energy of the exact functional for fractional-spin states
is a constant, equal to the energy of the comprising degenerate pure spin
states. Dramatic deviations from this exact constancy condition exist with all
approximate functionals, leading to large static correlation errors for
strongly correlated systems, such as chemical bond dissociation and band
structure of Mott insulators. This is demonstrated with numerical calculations
for several molecular systems. Approximating the constancy behavior for
fractional spins should be a major aim in functional constructions and should
open the frontier for DFT to describe strongly correlated systems. The key
results are also shown to apply in reduced density-matrix functional theory.Comment: 6 pages, 4 figure
Queen control of a key life-history event in a eusocial insect
In eusocial insects, inclusive fitness theory predicts potential queenâworker conflict over the timing of events in colony life history. Whether queens or workers control the timing of these events is poorly understood. In the bumble-bee Bombus terrestris, queens exhibit a âswitch pointâ in which they switch from laying diploid eggs yielding females (workers and new queens) to laying haploid eggs yielding males. By rearing foundress queens whose worker offspring were removed as pupae and sexing their eggs using microsatellite genotyping, we found that queens kept in the complete absence of adult workers still exhibit a switch point. Moreover, the timing of their switch points relative to the start of egg-laying did not differ significantly from that of queens allowed to produce normal colonies. The finding that bumble-bee queens can express the switch point in the absence of workers experimentally demonstrates queen control of a key life-history event in eusocial insects. In addition, we found no evidence that workers affect the timing of the switch point either directly or indirectly via providing cues to queens, suggesting that workers do not fully express their interests in queenâworker conflicts over colony life history
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