The Complexity of Planning Revisited - A Parameterized Analysis

The early classifications of the computational complexity of planning under various restrictions in STRIPS (Bylander) and SAS+ (Baeckstroem and Nebel) have influenced following research in planning in many ways. We go back and reanalyse their subclasses, but this time using the more modern tool of parameterized complexity analysis. This provides new results that together with the old results give a more detailed picture of the complexity landscape. We demonstrate separation results not possible with standard complexity theory, which contributes to explaining why certain cases of planning have seemed simpler in practice than theory has predicted. In particular, we show that certain restrictions of practical interest are tractable in the parameterized sense of the term, and that a simple heuristic is sufficient to make a well-known partial-order planner exploit this fact.Comment: (author's self-archived copy

Session A5: Dam Removal: Enhancing or Degrading Ecological Integrity?

Abstract: Removal of dams is increasingly being used to restore fragmented rivers and streams. The incentive is often to give migrating fish access to upstream spawning habitats, but dam removal may also bring other benefits, such as recovery of riparian vegetation and a more heterogeneous environment for aquatic invertebrates. Dam removal may also act as a disturbance on the system, releasing trapped sediments to downstream reaches. Depending on the amount of sediments in the former reservoir this disturbance may be transient or act over a longer time period. Whether dam removal is beneficial or not to the ecosystem may therefore depend on the type of organism. We have studied the effect of dam removal on riparian vegetation and benthic invertebrates in two Swedish streams over a period of 3 and 5 years respectively, and found that riparian vegetation generally benefitted from removal. Species richness increased, and species composition became more similar to a reference situation within a three year period. In contrast, benthic invertebrates seemed to be negatively affected by dam removal. While we saw no effects on community composition of benthic invertebrates, taxon richness decreased continuously over a five year period and total densities decreased initially but showed weak signs of recovery over the five year period. Our results also indicate that the response varies between invertebrate taxa

Refining complexity analyses in planning by exploiting the exponential time hypothesis

The use of computational complexity in planning, and in AI in general, has always been a disputed topic. A major problem with ordinary worst-case analyses is that they do not provide any quantitative information: they do not tell us much about the running time of concrete algorithms, nor do they tell us much about the running time of optimal algorithms. We address problems like this by presenting results based on the exponential time hypothesis (ETH), which is a widely accepted hypothesis concerning the time complexity of 3-SAT. By using this approach, we provide, for instance, almost matching upper and lower bounds onthe time complexity of propositional planning.Funding Agencies|National Graduate School in Computer Science (CUGS), Sweden; Swedish Research Council (VR) [621-2014-4086]</p

When is it biological control? A framework of definitions, mechanisms, and classifications

Biological control, or biocontrol, is the exploitation of living agents (incl. viruses) to combat pestilential organisms (incl. pathogens, pests, and weeds) for diverse purposes to provide human benefits. Thus, during the last century the practices and concepts involved have evolved in separate streams associated with distinct scientific and taxonomic disciplines. In parallel developments, there have been increasing references to biological control in industrial contexts and legislation, resulting in conceptual and terminological disintegration. The aim of this paper is to provide a global conceptual and terminological platform that facilitates future development of the field. We review use of previously suggested terms in key fields (e.g., phytopathology, entomology, and weed science), eliminate redundant terminology, identify three principles that should underpin the concept, and then present a new framework for biological control, rooted in seminal publications. The three principles establish that (1) only living agents can mediate biological control, (2) biological control always targets a pest, directly or indirectly, and (3) all biocontrol methods can be classified in four main categories depending on whether resident agents are utilized, with or without targeted human intervention (conservation biological control and natural biological control, respectively) or agents are added for permanent or temporary establishment (classical biological control and augmentative biological control, respectively). Correct identification of what is, and is not, biological control can help efforts to understand and optimize biological pest control for human and environmental benefits. The new conceptual framework may contribute to more uniform and appropriate regulatory approaches to biological control, and more efficient authorization and application of biocontrol products

Suspicion and treatment of severe sepsis. An overview of the prehospital chain of care

Sepsis is a life-threatening condition where the risk of death has been reported to be even higher than that associated with the major complications of atherosclerosis, i.e. myocardial infarction and stroke. In all three conditions, early treatment could limit organ dysfunction and thereby improve the prognosis

Optimal Swimming Speed in Head Currents and Effects on Distance Movement of Winter-Migrating Fish

Migration is a commonly described phenomenon in nature that is often caused by spatial and temporal differences in habitat quality. However, as migration requires energy, the timing of migration may depend not only on differences in habitat quality, but also on temporal variation in migration costs. Such variation can, for instance, arise from changes in wind or current velocity for migrating birds and fish, respectively. Whereas behavioural responses of birds to such changing environmental conditions have been relatively well described, this is not the case for fish, although fish migrations are both ecologically and economically important. We here use passive and active telemetry to study how winter migrating roach regulate swimming speed and distance travelled per day in response to variations in head current velocity. Furthermore, we provide theoretical predictions on optimal swimming speeds in head currents and relate these to our empirical results. We show that fish migrate farther on days with low current velocity, but travel at a greater ground speed on days with high current velocity. The latter result agrees with our predictions on optimal swimming speed in head currents, but disagrees with previously reported predictions suggesting that fish ground speed should not change with head current velocity. We suggest that this difference is due to different assumptions on fish swimming energetics. We conclude that fish are able to adjust both swimming speed and timing of swimming activity during migration to changes in head current velocity in order to minimize energy use

I fäders och mödrars spår. Landsortsungdomars identitetsutveckling och vuxenblivande i ett livsformsperspektiv.

Abstract Title: Following in their Father’s and Mother’s Path: Young people’s steps to adulthood in a Swedish municipal community from a life form perspective. Language: Swedish with an English summary, 280 pages. Author: Christer Jonsson Doctoral Dissertation at the Department of Sociology, University of Gothenburg, Box 720 SE-405 30 GÖTEBORG, Sweden ISBN: 978-91-975405-9-9, ISSN: 1650-4313 Gothenburg 2010. This dissertation examines young people, aged 16-24, their life expectations and steps towards adulthood. Life form analysis of their families plays a central role in understan- ding how social and cultural reproduction continues in traditional class-patterns in Swedish late modern society during the 1990’s. Theories of the ’individualized society’ are considered to have less validity for interpreting how these young people look at diffe- rent aspects of their everyday lives. In this study, five groups (types) of young people are distinguished. Four types demonstrate discernible patterns related to the career life form and the wage-labour life form. The young people with this two life-orientation were then separated according to gender for further interpretation. The fifth group of young people seems to be less connected with cultural socialisation in the family; their every-day engagements and their life expectations are devoted to a special interest. The empirical study, grounded in semi-structured interviews, focuses on growing-up in a Swe- dish rural community. Data was collected during a turbulent time in Swedish society. The first occasion of data collection took place at the beginning of the 1990’s when entering adult society had a relatively low threshold. The second occasion, the follow-up study some years later, took place when the unemployment rates of the 1990’s economic crises had reached their summit. This societal changes complicated, particularly for the wage labour-oriented, young people’s integration into adult society. Keywords: Youth, young people, life form, life expectations, social and cultural repro- duction