2,264 research outputs found
Understanding Algorithm Performance on an Oversubscribed Scheduling Application
The best performing algorithms for a particular oversubscribed scheduling
application, Air Force Satellite Control Network (AFSCN) scheduling, appear to
have little in common. Yet, through careful experimentation and modeling of
performance in real problem instances, we can relate characteristics of the
best algorithms to characteristics of the application. In particular, we find
that plateaus dominate the search spaces (thus favoring algorithms that make
larger changes to solutions) and that some randomization in exploration is
critical to good performance (due to the lack of gradient information on the
plateaus). Based on our explanations of algorithm performance, we develop a new
algorithm that combines characteristics of the best performers; the new
algorithms performance is better than the previous best. We show how hypothesis
driven experimentation and search modeling can both explain algorithm
performance and motivate the design of a new algorithm
Improved sampling of the pareto-front in multiobjective genetic optimizations by steady-state evolution: a Pareto converging genetic algorithm
Previous work on multiobjective genetic algorithms has been focused on preventing genetic drift and the issue of convergence has been given little attention. In this paper, we present a simple steady-state strategy, Pareto Converging Genetic Algorithm (PCGA), which naturally samples the solution space and ensures population advancement towards the Pareto-front. PCGA eliminates the need for sharing/niching and thus minimizes heuristically chosen parameters and procedures. A systematic approach based on histograms of rank is introduced for assessing convergence to the Pareto-front, which, by definition, is unknown in most real search problems.
We argue that there is always a certain inheritance of genetic material belonging to a population, and there is unlikely to be any significant gain beyond some point; a stopping criterion where terminating the computation is suggested. For further encouraging diversity and competition, a nonmigrating island model may optionally be used; this approach is particularly suited to many difficult (real-world) problems, which have a tendency to get stuck at (unknown) local minima. Results on three benchmark problems are presented and compared with those of earlier approaches. PCGA is found to produce diverse sampling of the Pareto-front without niching and with significantly less computational effort
Linking Search Space Structure, Run-Time Dynamics, and Problem Difficulty: A Step Toward Demystifying Tabu Search
Tabu search is one of the most effective heuristics for locating high-quality
solutions to a diverse array of NP-hard combinatorial optimization problems.
Despite the widespread success of tabu search, researchers have a poor
understanding of many key theoretical aspects of this algorithm, including
models of the high-level run-time dynamics and identification of those search
space features that influence problem difficulty. We consider these questions
in the context of the job-shop scheduling problem (JSP), a domain where tabu
search algorithms have been shown to be remarkably effective. Previously, we
demonstrated that the mean distance between random local optima and the nearest
optimal solution is highly correlated with problem difficulty for a well-known
tabu search algorithm for the JSP introduced by Taillard. In this paper, we
discuss various shortcomings of this measure and develop a new model of problem
difficulty that corrects these deficiencies. We show that Taillards algorithm
can be modeled with high fidelity as a simple variant of a straightforward
random walk. The random walk model accounts for nearly all of the variability
in the cost required to locate both optimal and sub-optimal solutions to random
JSPs, and provides an explanation for differences in the difficulty of random
versus structured JSPs. Finally, we discuss and empirically substantiate two
novel predictions regarding tabu search algorithm behavior. First, the method
for constructing the initial solution is highly unlikely to impact the
performance of tabu search. Second, tabu tenure should be selected to be as
small as possible while simultaneously avoiding search stagnation; values
larger than necessary lead to significant degradations in performance
How energy and water availability constrain vegetation water-use along the North Australian Tropical Transect
© 2016, Gorgan Univ Agricultural Sciences and Natural Resources. All rights reserved. Energy and water availability were identified as the first order controls of evapotranspiration (ET) in ecohyrodrology. With a ~1,000 km precipitation gradient and distinct wet-dry climate, the North Australian Tropical Transect (NATT) was well suited for evaluating how energy and water availabilities constrain water use by vegetation, but has not been done yet. In this study, we addressed this question using Budyko framework that quantifies the evapotranspiration as a function of energy-limited rate and precipitation. Path analysis was adopted to evaluate the dependencies of water and carbon fluxes on ecohydrological variables. Results showed that the major drivers of water and carbon fluxes varied between wet and dry savannas: down-welling solar radiation was the primary driver of the wet season ET in mesic savanna ecosystems, while soil water availability was the primary driver in inland dryland ecosystems. Vegetation can significantly regulate water and carbon fluxes of savanna ecosystems, as supported by the strong link of LAI with ET and GPP from path analysis. Vegetation structure (i.e. the tree:grass ratio) at each site can regulate the impact of climatic constraint on ET and GPP. Sites with a low tree:grass ratio had ET and GPP that exceeded sites with high a tree:grass ratio when the grassy understory was active. Identifying the relative importance of these climate drivers and vegetation structure on seasonal patterns of water use by these ecosystems will help us decide our priorities when improving the estimates of ET and GPP
Innovation as a Nonlinear Process, the Scientometric Perspective, and the Specification of an "Innovation Opportunities Explorer"
The process of innovation follows non-linear patterns across the domains of
science, technology, and the economy. Novel bibliometric mapping techniques can
be used to investigate and represent distinctive, but complementary
perspectives on the innovation process (e.g., "demand" and "supply") as well as
the interactions among these perspectives. The perspectives can be represented
as "continents" of data related to varying extents over time. For example, the
different branches of Medical Subject Headings (MeSH) in the Medline database
provide sources of such perspectives (e.g., "Diseases" versus "Drugs and
Chemicals"). The multiple-perspective approach enables us to reconstruct facets
of the dynamics of innovation, in terms of selection mechanisms shaping
localizable trajectories and/or resulting in more globalized regimes. By
expanding the data with patents and scholarly publications, we demonstrate the
use of this multi-perspective approach in the case of RNA Interference (RNAi).
The possibility to develop an "Innovation Opportunities Explorer" is specified.Comment: Technology Analysis and Strategic Management (forthcoming in 2013
Loneliness, social relations and health and wellbeing in deprived communities
There is growing policy concern about the extent of loneliness in advanced societies, and its
prevalence among various social groups. This study looks at loneliness among people living in
deprived communities, where there may be additional barriers to social engagement including low
incomes, fear of crime, poor services and transient populations. The aim was to examine the
prevalence of loneliness, and also its associations with different types of social contacts and forms of
social support, and its links to self-reported health and wellbeing in the population group. The
method involved a cross-sectional survey of 4,302 adults across 15 communities, with the data
analysed using multinomial logistic regression controlling for sociodemographics, then for all other
predictors within each domain of interest. Frequent feelings of loneliness were more common
among those who: had contact with family monthly or less; had contact with neighbours weekly or
less; rarely talked to people in the neighbourhood; and who had no available sources of practical or
emotional support. Feelings of loneliness were most strongly associated with poor mental health,
but were also associated with long-term problems of stress, anxiety and depression, and with low
mental wellbeing, though to a lesser degree. The findings are consistent with a view that situational
loneliness may be the product of residential structures and resources in deprived areas. The findings
also show that neighbourly behaviours of different kinds are important for protecting against
loneliness in deprived communities. Familiarity within the neighbourhood, as active acquaintance
rather than merely recognition, is also important. The findings are indicative of several mechanisms
that may link loneliness to health and wellbeing in our study group: loneliness itself as a stressor;
lonely people not responding well to the many other stressors in deprived areas; and loneliness as
the product of weak social buffering to protect against stressors
Adaptive mutation using statistics mechanism for genetic algorithms
Copyright @ 2004 Springer-Verla
ACVIM consensus statement on the treatment of immune-mediated hemolytic anemia in dogs
Immune‐mediated hemolytic anemia (IMHA) causes severe anemia in dogs and is associated with considerable morbidity and mortality. Treatment with various immunosuppressive and antithrombotic drugs has been described anecdotally and in previous studies, but little consensus exists among veterinarians as to the optimal regimen to employ and maintain after diagnosis of the disease. To address this inconsistency and provide evidence‐based guidelines for treatment of IMHA in dogs, we identified and extracted data from studies published in the veterinary literature. We developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria, explanation of treatment regimens, and validity of statistical methods. In combination with our clinical experience and comparable guidelines for humans afflicted with autoimmune hemolytic anemia, we used the conclusions of this process to make a set of clinical recommendations regarding treatment of IMHA in dogs, which we refined subsequently by conducting several iterations of Delphi review. Additionally, we considered emerging treatments for IMHA in dogs and highlighted areas deserving of future research. Comments were solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted for publication. The resulting document is intended to provide clinical guidelines for management of IMHA in dogs. These guidelines should be implemented pragmatically, with consideration of animal, owner, and veterinary factors that may vary among cases
"Meaning" as a sociological concept: A review of the modeling, mapping, and simulation of the communication of knowledge and meaning
The development of discursive knowledge presumes the communication of meaning
as analytically different from the communication of information. Knowledge can
then be considered as a meaning which makes a difference. Whereas the
communication of information is studied in the information sciences and
scientometrics, the communication of meaning has been central to Luhmann's
attempts to make the theory of autopoiesis relevant for sociology. Analytical
techniques such as semantic maps and the simulation of anticipatory systems
enable us to operationalize the distinctions which Luhmann proposed as relevant
to the elaboration of Husserl's "horizons of meaning" in empirical research:
interactions among communications, the organization of meaning in
instantiations, and the self-organization of interhuman communication in terms
of symbolically generalized media such as truth, love, and power. Horizons of
meaning, however, remain uncertain orders of expectations, and one should
caution against reification from the meta-biological perspective of systems
theory
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