Simulating the use of macro-actions through action reordering

The use of macro-actions in planning introduces a trade-off.. Macro-actions can offer search guidance by suggesting sequences of actions; but can potentially make search more expensive by increasing the branching factor. In this paper we present a technique for simulating the use of macro actions by altering the order in which actions are considered for application during enforced hill-climbing search. Actions are ordered based on the number of times they have occurred, in past solution plans, following the last action added to the plan. We demonstrate that the action-reordering technique used can offer improved search performance without the negative performance impacts often observed when using macro-actions

An investigation into the concept of and factors leading to impact creep and its management

This study defines and explores the nature of impact creep within the context of two contrasting case studies. The methods applied in undertaking this study consisted of a literature review and development and distribution of questionnaires to visitors at Monkey Mia and an interview of managers at Monkey Mia and Tree Top Walk. The project considered impact creep relevant to both public and private facility developments. Impact creep can be defined as a temporal sequence of changes that lead to a site being more developed. These changes confer both negative and positive impacts. Each impact creep situation may be deemed unique according to different tourism situations and attractions. Both Tree Top Walk and Monkey Mia have a history of increasing visitation which has increased the potential for further impacts. Management has responded accordingly and the resultant actions have reduced negative environmental impacts through site hardening and associated developments. The resultant development in turn appears to have contributed to an increased attractiveness for a wider visitor profile. At both Monkey Mia and the Tree Top Walk increasing visitor numbers were not an immediate concern. Generally visitors to both sites are predominantly first time visitors on a multi-destination trip. Visitors to these sites are most likely to visit in family groups or with friends of two to four persons, aged in the 25 to 49 year age bracket. In both surveys there were a higher proportion of females to males. At Monkey Mia, the majority of respondents are from overseas and Western Australia with the lowest proportion from interstate. In contrast, at Tree Top Walk, the proportion of overseas, Western Australia and interstate visitors was fairly even. Respondents were most likely to travel to the respective regions in passenger vehicles and generally stay for short visits (less than a week). The main attraction for respondents was the natural area attraction, i.e. dolphins at Monkey Mia and the Tingle forest/Tree Top Walk at the Valley of the Giants. The Monkey Mia visitor survey was also used to determine if management actions of site hardening detract from the visitor experience and to determine how visitors feel about highly developed sites such as those that contain permanent accommodation facilities and infrastructure. The survey revealed that visitors generally prefer natural landscapes with limited facilities. However, the facilities provided were not seen as being detractive and had no influence on the quality of the visit. Moreover, facilities may be considered as a positive influence because of the convenience they offer. A major difference between the two case studies is that impact creep has occurred according to different policy directives. Tree Top Walk was developed under a management plan that had clear guidelines. Monkey Mia had no management plan and joint management with the Shire of Shark Bay. When accommodation facilities were developed at Monkey Mia, the Western Australian Department of Conservation and Land Management (CALM) recommendations were ignored in favour for economic returns and political pressure. A notable difference between the two sites, therefore, is that Tree Top Walk has no accommodation facility so the visitation period is short, while Monkey Mia has accommodation which means that limiting visitor use is problematic because as many as 600 people stay in the vicinity of the interaction area overnight. For Tree Top Walk a dispersal strategy in the form of a visitor centre may help to focus attention away from the main attraction during busy periods and during wait times if restrictions are operating due to heavy demand. Because of the potential for increased visitation, crowding, conflicts and reduced visitor satisfaction at Monkey Mia limitations on use may have to be applied. Previous work has shown that use/access restrictions, in the form of a reservation or permit system, may be the best approach

Planning in probabilistic domains using a deterministic numeric planner

In the probabilistic track of the IPC5 - the last International planning competitions - a probabilistic planner based on combining deterministic planning with replanning - FF-REPLAN - out performed the other competitors. This probabilistic planning paradigm discarded the probabilistic information of the domain, just considering for each action its nominal effect as a deterministic effect

VLF, magnetic bay and Pi2 substorm signatures at auroral and midlatitude ground stations

A superposed epoch analysis of 100–300 substorms is performed to determine the median size and shape of the substorm-associated VLF chorus, magnetic bay, and Pi2 pulsation burst observed at the near-auroral Halley research station, Antarctica, and at the midlatitude Faraday station at three different local times (2230, 2330, 0130 MLT). The spatial and temporal properties of the magnetic bay signatures are compared with the University of York implementation of the Kisabeth–Rostoker substorm current wedge (SCW) model and the Weimer pulse model, respectively. These constitute the best analytical models of the substorm to date. It is shown that the polarities and relative amplitudes of the observed magnetic bays in the H, D, and Z components at Halley at midnight MLT and at Faraday in the premidnight sector are consistent with the York model for a SCW 3 hours wide in MLT with its westward electrojet at 67°S magnetic latitude. In particular the little-discussed Z component of the bay agrees with the model and is shown to be the clearest substorm signature of the three components, especially at midlatitude. The midnight and postmidnight bays are similar to the premidnight case but progressively smaller and cannot be fully reconciled with the model. The shape of the H and Z bays at Halley and the D bays at Faraday fit a normalized Weimer pulse well, with Weimer's 2 h−1 recovery rate, but the other components do not. The D component at Halley and H at Faraday do fit the Weimer pulse shape but with a faster recovery rate of 4 h−1. It is proposed that this is due to the effect of a decaying current in the SCW combining with the geometrical effect of changing SCW configuration and position relative to the observing station. The Z component at Faraday recovers more slowly than the 2 h−1 Weimer prediction; we cannot explain this. Secondary bays at Halley and Faraday show a clear tendency to recur after 2 hours. Inflection points just prior to onset at Halley and Faraday are argued to be related to reduced convection associated with northward turning of the IMF. The median substorm signature at Halley in the Pi2 frequency band (7–25 mHz) is well correlated with the bay structure, showing that it is part of a broader band, possibly turbulent, spectrum in the substorm-dependent DP2 current. There is evidence of a minor additional narrow band component occurring at substorm onset. This is the dominant signal at Faraday which shows the classic midlatitude substorm signature, a short Pi2 pulsation burst at onset, that decreases progressively in intensity with increasing local time, implying a source region biased to the evening side or else preferred propagation to the east from a near-midnight source

Water, water everywhere but not a drop to drink?

Biofilms are emerging as an increasing problem as medical technology advances. Dental practice is no exception and interest in the role of biofilms within dental units as a possible source of cross-infection is intensifying. It is difficult to quantitate the risks associated with aerosolised bacteria for the majority of patients seen in general practice. However, it seems prudent to eliminate this source of infection during treatment of compromised patients. This article attempts to provide a brief overview of current concepts and problems in this area of infection control

A spatial analysis of physiological changes associated with infection of cotyledons of marrow plants with cucumber mosaic virus

Changes in host primary metabolism associated with the compatible interaction between cucumber mosaic virus and cotyledons of the marrow plant (Cucurbita pepo L.) have been localized, first by measuring activities of key enzymes in infected and uninfected regions of the cotyledon, and second by histochemical techniques applied to tissue prints of the infected region. A series of progressive metabolic changes occurs within the expanding infected lesion. Virus replication and the synthesis of viral protein at the periphery creates a strong sink demand associated with increased activities of anaplerotic enzymes, increased photosynthesis, and starch accumulation. Inside the lesion, when the synthesis of virus has declined, photosynthesis is reduced, starch is mobilized, and the emphasis of metabolism is shifted toward glycolysis and mitochondrial respiration. These changes are associated spatially with the onset of chlorosis. A decrease in total protein synthesis in this inner zone could be instrumental in some or all of these changes, leading to symptoms of viral infection

The role of phosphatidyl-glycerol in the determination of fetal lung maturity

Phosphatidyl-glycerot (PG) and the lecithin/sphingomyelin (LIS) ratio were determined on amniotic fluid from 140 patients to evaluate the role of PG estimation as a functional fetal lung maturity test. PG was absent without associated respiratory distress syndrome (RDS) in 17 cases (12%).and present in 123; 3 of the infants born to these patients developed slight hyaline membrane disease. There were no neonatal deaths. When both PG and the LIS ratio were determined the accuracy of prediction of the RDS improved from 87% to 93%. PG determination should not be used as a substitute for the LIS ratio, butshould be used in conjunction with it in high-risk situations

Origin of fluids in the shallow geothermal environment of Savo, Solomon Islands.

Savo is a recently emergent volcano. An active geothermal system has been present for at least 50 years, expressed at the surface by numerous hot springs, fumaroles and steaming ground. Samples of water and steam were collected from geothermal features and non-thermal springs and wells, and representative samples of altered rocks and precipitates were collected from geothermal areas. Analysis of the waters for anion, cation and stable isotope composition shows that the waters discharging at the surface fall into two groups Reoka type fluids have the high sulfate, low pH, and enriched δ18O and δD values typical of steam heated acid sulfate waters, where shallow groundwater is heated by rising steam and gas. Isotopically light H2S is oxidised in the near surface environment to produce the sulfate content. Rembokola type fluids have chemistry distinct from the Reoka type fluids, despite the two being found within close proximity (<10 m). Rembokola Type fluids produce a carbonate sinter, so are assumed to be saturated with bicarbonate. The aqueous sulfate has heavy δ34S, suggesting that it is not exclusively produced by the oxidation of H2S in the near surface environment. We suggest that condensation of volcanic gases (including CO2 and isotopically heavy SO2) into meteoric-derived groundwater in the upper levels of the volcanic edifice produces these carbonate–sulfate waters. The presence of SO2 suggests that there is a degassing magma at depth, and potentially a high sulfidation-type epithermal system beneath the steam heated zone