FLECS: Planning with a Flexible Commitment Strategy

There has been evidence that least-commitment planners can efficiently handle planning problems that involve difficult goal interactions. This evidence has led to the common belief that delayed-commitment is the "best" possible planning strategy. However, we recently found evidence that eager-commitment planners can handle a variety of planning problems more efficiently, in particular those with difficult operator choices. Resigned to the futility of trying to find a universally successful planning strategy, we devised a planner that can be used to study which domains and problems are best for which planning strategies. In this article we introduce this new planning algorithm, FLECS, which uses a FLExible Commitment Strategy with respect to plan-step orderings. It is able to use any strategy from delayed-commitment to eager-commitment. The combination of delayed and eager operator-ordering commitments allows FLECS to take advantage of the benefits of explicitly using a simulated execution state and reasoning about planning constraints. FLECS can vary its commitment strategy across different problems and domains, and also during the course of a single planning problem. FLECS represents a novel contribution to planning in that it explicitly provides the choice of which commitment strategy to use while planning. FLECS provides a framework to investigate the mapping from planning domains and problems to efficient planning strategies.Comment: See http://www.jair.org/ for an online appendix and other files accompanying this articl

Luttinger States at the Edge

An effective wavefunction for the edge excitations in the Fractional quantum Hall effect can be found by dimensionally reducing the bulk wavefunction. Treated this way the Laughlin $\nu=1/(2n+1)$ wavefunction yields a Luttinger model ground state. We identify the edge-electron field with a Luttinger hyper-fermion operator, and the edge electron itself with a non-backscattering Bogoliubov quasi-particle. The edge-electron propagator may be calculated directly from the effective wavefunction using the properties of a one-dimensional one-component plasma, provided a prescription is adopted which is sensitive to the extra flux attached to the electrons

A Dynamical Potential-Density Pair for Star Clusters With Nearly Isothermal Interiors

We present a potential-density pair designed to model nearly isothermal star clusters (and similar self-gravitating systems) with a central core and an outer turnover radius, beyond which density falls off as $r^{-4}$. In the intermediate zone, the profile is similar to that of an isothermal sphere (density $\rho \propto r^{-2}$), somewhat less steep than the King 62 profile, and with the advantage that many dynamical quantities can be written in a simple closed form. We derive new analytic expressions for the cluster binding energy and velocity dispersion, and apply these to create toy models for cluster core collapse and evaporation. We fit our projected surface brightness profiles to observed globular and open clusters, and find that the quality of the fit is generally at least as good as that for the surface brightness profiles of King 62. This model can be used for convenient computation of the dynamics and evolution of globular and nuclear star clusters.Comment: 6 pages, 5 figures. Published in ApJL; changes to match published versio

Base metal mineralisation associated with Ordovician shales in south-west Scotland

Several narrow, lenticular belts of black cherty mudstone and siltstone (the Moffat Shales), alternating with thick greywacke sequences, strike north-east to south-west across Galloway with uniformly steep dip. In the Penkiln Burn area, 13 km NNE of Newton Stewart, one such belt is hornfelsed and considerably broadened near the southwest margin of the Loch Doon granitic pluton. Base metal anomalies in drainage and overburden are spatially associated with the broadened section of the shale belt, which is host to weakly disseminated and epigenetic Pb-Zn-Cu mineralisation. Within the Moffat Shale sequence highly siliceous mudstone and siltstone are interbedded with chert, greywacke and possibly thin tuffaceous horizons. The broadening is structurally controlled, caused by the interference of early structures with a major reciined fold plunging to the south-east. Several phases of faulting and minor intrusion have been recognised, and the abundance of dykes is an unusual geological feature of the area. Lead is particularly enriched in drainage samples, reaching approximately 1% in pan concentrates collected close to a mineralised gossan-like zone. The main leadbearing mineral identified in the anomalous concentrates, and the in situ gossan material, is the secondary lead phosphate plumbogummite. Overburden sampling proved anomalous metal values extending for 2.3 km along strike and 500 m across strike. Lead again shows the greatest enrichment, with values ranging up to about 0.5 % , in soil close to the gossan. Zinc and copper give a weaker response in both overburden and drainage, but drilling showed that zinc, in the form of disseminated sphalerite, has a greater incidence at depth than was suggested by the surface anomalies. Three varieties of mineralisation have been recognised. The earliest consists of fine disseminations, chiefly of sphalerite and pyrite, in the hornfelsed sediments. It is characterised by zinc levels between 500 and 1000 ppm over several metres of drill core; lead levels rarely exceed 300 ppm. The second phase of mineralisation occurs in thin quartz veinlets, which in this case contain accessory sphalerite, galena and pyrite. Where the veining is intense, lead concentrations reach 7000 ppm and those of zinc 1500 ppm, but these values persist over only a few tens of cm of core. Finally, a low-temperature mineral assemblage in which plumbogummite is dominant is associated with the altered margins of dykes and gossanlike zones occupying a north-south fault system. Lead levels in the dyke margins range up to 1.5 % in zones generally less than 50 cm thick, but 4.5 %I Pb has been recorded in one specimen from the exposed gossan. Fine stratiform pyrite iaminae in mudstone interbedded with chert containing disseminated pyrite and sphalerite suggests that at leas: some of the early mineralisation is synsedimentary. Later mineralisation phases are, however, structurally controlled and the origin of the majority of the base metal mineralisation remains problematical. The unusual abundance of minor intrusions in the mineralised zone is strong circumstantial evidence for an igneous source. Full details of the soil geochemical surveys and the geophysical surveys are available for inspection at the Keyworth office of BGS

Latitude variation of recurrent fluxes in the outer solar system

Recurrent low energy (greater than or = to 0.5 MeV) proton flux enhancements, reliable indicators of corotating plasma interaction regions, were observed on the Voyager 1 and 2 and Pioneer 11 spacecraft in the heliographic latitude range 2 deg S to 23 N and the heliocentric radial range 11 to 20 AU. After a period of rather high correlation between fluxes at different latitudes in early 1983, distinct differences developed in the fluxes during an overall flux decrease. The flux intensities returned to higher levels in early 1984 and differences in both the recurrence frequency and flux intensity persisted into 1985, as Voyager 1 traveled to 23 AU and 25 N latitude. Intercomparison of data from the three spacecraft indicates that the flux differences are most likely due to latitudinal rather than radial or temporal variations

Effect of hydraulic fluid (MIL-H-83282) on selected commercial O-ring compounds

Acrylonitrile and fluorocarbon compounds were evaluated at various temperatures and time intervals in samples of the fluid obtained from three qualified suppliers. It was concluded that both polymers can function in hydraulic fluids within the conditions defined by this study. Hydraulic fluid from each manufacturer was similar in its effect upon each given O-ring material, with one exception. Similarly, there were no striking differences in the resistance of O-rings of the same generic rubber type when provided by the different manufacturers

New battery model and state-of-health determination through subspace parameter estimation and state-observer techniques

This paper describes a novel adaptive battery model based on a remapped variant of the well-known Randles' lead-acid model. Remapping of the model is shown to allow improved modeling capabilities and accurate estimates of dynamic circuit parameters when used with subspace parameter-estimation techniques. The performance of the proposed methodology is demonstrated by application to batteries for an all-electric personal rapid transit vehicle from the Urban Light TRAnsport (ULTRA) program, which is designated for use at Heathrow Airport, U. K. The advantages of the proposed model over the Randles' circuit are demonstrated by comparisons with alternative observer/estimator techniques, such as the basic Utkin observer and the Kalman estimator. These techniques correctly identify and converge on voltages associated with the battery state-of-charge (SoC), despite erroneous initial conditions, thereby overcoming problems attributed to SoC drift (incurred by Coulomb-counting methods due to overcharging or ambient temperature fluctuations). Observation of these voltages, as well as online monitoring of the degradation of the estimated dynamic model parameters, allows battery aging (state-of-health) to also be assessed and, thereby, cell failure to be predicted. Due to the adaptive nature of the proposed algorithms, the techniques are suitable for applications over a wide range of operating environments, including large ambient temperature variations. Moreover, alternative battery topologies may also be accommodated by the automatic adjustment of the underlying state-space models used in both the parameter-estimation and observer/estimator stages