290,257 research outputs found
Wrapper Maintenance: A Machine Learning Approach
The proliferation of online information sources has led to an increased use
of wrappers for extracting data from Web sources. While most of the previous
research has focused on quick and efficient generation of wrappers, the
development of tools for wrapper maintenance has received less attention. This
is an important research problem because Web sources often change in ways that
prevent the wrappers from extracting data correctly. We present an efficient
algorithm that learns structural information about data from positive examples
alone. We describe how this information can be used for two wrapper maintenance
applications: wrapper verification and reinduction. The wrapper verification
system detects when a wrapper is not extracting correct data, usually because
the Web source has changed its format. The reinduction algorithm automatically
recovers from changes in the Web source by identifying data on Web pages so
that a new wrapper may be generated for this source. To validate our approach,
we monitored 27 wrappers over a period of a year. The verification algorithm
correctly discovered 35 of the 37 wrapper changes, and made 16 mistakes,
resulting in precision of 0.73 and recall of 0.95. We validated the reinduction
algorithm on ten Web sources. We were able to successfully reinduce the
wrappers, obtaining precision and recall values of 0.90 and 0.80 on the data
extraction task
More than one way to see it: Individual heuristics in avian visual computation
Comparative pattern learning experiments investigate how different species find regularities in sensory input, providing insights into cognitive processing in humans and other animals. Past research has focused either on one species’ ability to process pattern classes or different species’ performance in recognizing the same pattern, with little attention to individual and species-specific heuristics and decision strategies. We trained and tested two bird species, pigeons (Columba livia) and kea (Nestor notabilis, a parrot species), on visual patterns using touch-screen technology. Patterns were composed of several abstract elements and had varying degrees of structural complexity. We developed a model selection paradigm, based on regular expressions, that allowed us to reconstruct the specific decision strategies and cognitive heuristics adopted by a given individual in our task. Individual birds showed considerable differences in the number, type and heterogeneity of heuristic strategies adopted. Birds’ choices also exhibited consistent species-level differences. Kea adopted effective heuristic strategies, based on matching learned bigrams to stimulus edges. Individual pigeons, in contrast, adopted an idiosyncratic mix of strategies that included local transition probabilities and global string similarity. Although performance was above chance and quite high for kea, no individual of either species provided clear evidence of learning exactly the rule used to generate the training stimuli. Our results show that similar behavioral outcomes can be achieved using dramatically different strategies and highlight the dangers of combining multiple individuals in a group analysis. These findings, and our general approach, have implications for the design of future pattern learning experiments, and the interpretation of comparative cognition research more generally
Evidence of swarm intelligence in collective cultures: Identifying the use of the swarm goal directive of productivity in Pacific organisation systems as well as getween genders
Intrigued by the existence of societies outside that of the human population, scientists have ventured to study social aggregations within insects to seek insights on effective colonizing. The most popular of these social aggregations are colonies of ants and bees. In studying these groups of social insects researchers have developed algorithms loosely termed swarm intelligence that increase work efficiency within businesses and other social organizations (Bonabeau & Meyer, 2001). A subsequent proliferation of research in surrounding fields has allowed for investigation of key variables that improve work on a global scale (Bonabeau & Meyer, 2001). James Kennedy (1999), an initiator of swarm research, has suggested that there is a high correlation between systems that rely on each other for information and greater task accomplishment
Generating branes via sigma-models
Starting with the D-dimensional Einstein-dilaton-antisymmetric form equations
and assuming a block-diagonal form of a metric we derive a -dimensional
-model with the target space or its non-compact form. Various solution-generating techniques are
developed and applied to construct some known and some new -brane solutions.
It is shown that the Harrison transformation belonging to the
subgroup generates black -branes from the seed Schwarzschild solution. A
fluxbrane generalizing the Bonnor-Melvin-Gibbons-Maeda solution is constructed
as well as a non-linear superposition of the fluxbrane and a spherical black
hole. A new simple way to endow branes with additional internal structure such
as plane waves is suggested. Applying the harmonic maps technique we generate
new solutions with a non-trivial shell structure in the transverse space
(`matrioshka' -branes). It is shown that the -brane intersection rules
have a simple geometric interpretation as conditions ensuring the symmetric
space property of the target space. Finally, a Bonnor-type symmetry is used to
construct a new magnetic 6-brane with a dipole moment in the ten-dimensional
IIA theory.Comment: 21 pages Late
Type II Duality Symmetries in Six Dimensions
We discuss the different discrete duality symmetries in six dimensions that
act within and between (i) the 10-dimensional heterotic string compactified on
, (ii) the 10-dimensional Type IIA string compactified on and (iii)
the 10-dimensional Type IIB string compactified on . In particular we show
that the underlying group-theoretical structure of these discrete duality
symmetries is determined by the proper cubic group . Our group
theoretical interpretation leads to simple rules for constructing the explicit
form of the different discrete Type II duality symmetries in an arbitrary
background. The explicit duality rules we obtain are applied to construct dual
versions of the 6-dimensional chiral null model.Comment: 31 pages, 6 figures, epsfig.sty, late
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