Learning First-Order Definitions of Functions

First-order learning involves finding a clause-form definition of a relation from examples of the relation and relevant background information. In this paper, a particular first-order learning system is modified to customize it for finding definitions of functional relations. This restriction leads to faster learning times and, in some cases, to definitions that have higher predictive accuracy. Other first-order learning systems might benefit from similar specialization.Comment: See http://www.jair.org/ for any accompanying file

Unitary groups over local rings

Structural properties of unitary groups over local, not necessarily commutative, rings are developed, with applications to the computation of the orders of these groups (when finite) and to the degrees of the irreducible constituents of the Weil representation of a unitary group associated to a ramified extension of finite local rings

Improved Use of Continuous Attributes in C4.5

A reported weakness of C4.5 in domains with continuous attributes is addressed by modifying the formation and evaluation of tests on continuous attributes. An MDL-inspired penalty is applied to such tests, eliminating some of them from consideration and altering the relative desirability of all tests. Empirical trials show that the modifications lead to smaller decision trees with higher predictive accuracies. Results also confirm that a new version of C4.5 incorporating these changes is superior to recent approaches that use global discretization and that construct small trees with multi-interval splits.Comment: See http://www.jair.org/ for any accompanying file

An intelligent assistant for exploratory data analysis

In this paper we present an account of the main features of SNOUT, an intelligent assistant for exploratory data analysis (EDA) of social science survey data that incorporates a range of data mining techniques. EDA has much in common with existing data mining techniques: its main objective is to help an investigator reach an understanding of the important relationships ina data set rather than simply develop predictive models for selectd variables. Brief descriptions of a number of novel techniques developed for use in SNOUT are presented. These include heuristic variable level inference and classification, automatic category formation, the use of similarity trees to identify groups of related variables, interactive decision tree construction and model selection using a genetic algorithm

Benthic Biomonitoring in Arctic Tundra Streams: A Community-Based Approach in Iqaluit, Nunavut, Canada

Recent residential, commercial, and industrial development in the catchments of several Arctic streams has heightened the need to assess these freshwater systems accurately. It was imperative to develop methods that would be both effective at judging ecological condition of tundra streams and suitable for use by local groups. An investigation of two streams influenced by urbanization in Iqaluit, Nunavut, was carried out between July and August each year in 2007 – 09. Simple summary metrics (e.g., Shannon Index) and multivariate analysis (DCA, RD A) both demonstrated biological impairment in the benthic community at site locations downstream of urbanized portions of a local stream. This impairment was characterized by a loss of diversity and a dramatic shift of the benthic community to one dominated by chironomids from the subfamily Orthocladiinae. Elevated levels of total nitrogen (TN) and total phosphorus (TP) and several metals (Zn, Sr, Rb, Al, Co, Fe) were also found to be significantly related to benthic assemblages within these disturbed areas. This investigation also addressed taxonomic sufficiency, indicating that while family-level taxonomic identifications were sensitive enough to differentiate between pristine and impacted stream sites, a more precise taxonomic identification of the dominant benthos taxa (Insecta: Diptera: Chironomidae) to sub-family/tribe level identified a significant shift towards pollution-tolerant taxa. This higher taxonomic resolution will allow for the adaptation of protocols and the use of simple summary metrics to be effective for a community-based biomonitoring program in Arctic tundra streams.De récents développements résidentiels, commerciaux et industriels dans les bassins versants de plusieurs cours d’eau de l’Arctique ont intensifié la nécessité de bien évaluer ces systèmes d’eau douce. Il était impératif de mettre au point des méthodes qui permettraient de juger des conditions écologiques des cours d’eau de la toundra et qui seraient utilisables par divers groupes de la région. Entre juillet et août des années 2007 à 2009, une enquête a été effectuée sur deux cours d’eau influencés par l’urbanisation à Iqaluit, au Nunavut. De simples mesures sommaires (indice de Shannon par exemple) et une analyse à variables multiples (DCA, RDA) ont permis de démontrer la dégradation biologique de la communauté benthique à divers lieux du site, en aval de segments urbanisés d’un cours d’eau local. Cette dégradation était caractérisée par une perte de diversité et un changement dramatique de la communauté benthique qui est maintenant dominée par des chironomidés de la sous-famille Orthocladiinae. Nous avons également constaté que les taux élevés d’azote total (AT), de phosphore total (PT) et de plusieurs métaux (Zn, Sr, Rb, Al, Co, Fe) étaient fortement liés aux assemblages benthiques faisant partie de ces zones perturbées. Cette enquête a également porté sur la suffisance taxonomique, ce qui a laissé croire que bien que les identifications taxonomiques au niveau de la famille étaient assez sensibles pour différencier entre les sites de cours d’eau vierges et les sites perturbés, une identification taxonomique plus précise allant des taxons benthiques dominants (Insecta:Diptera: Chironomidae) jusqu’au niveau de la sous-famille et de la tribu ont permis d’identifier un virage important vers des taxons tolérants à la pollution. Cette résolution taxonomique supérieure permettra l’adaptation de protocoles et l’utilisation de simples mesures sommaires efficaces en vue de l’établissement d’un programme de biosurveillance communautaire dans les cours d’eau de la toundra de l’Arctique

A Hybrid N-body--Coagulation Code for Planet Formation

We describe a hybrid algorithm to calculate the formation of planets from an initial ensemble of planetesimals. The algorithm uses a coagulation code to treat the growth of planetesimals into oligarchs and explicit N-body calculations to follow the evolution of oligarchs into planets. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. Several complete calculations of terrestrial planet formation with the hybrid code yield good agreement with previously published calculations. These results demonstrate that the hybrid code provides an accurate treatment of the evolution of planetesimals into planets.Comment: Astronomical Journal, accepted; 33 pages + 11 figure

Mild sonochemical exfoliation of bromine-intercalated graphite: a new route towards graphene

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br(2) into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 mu m, corresponding to the grain size of the starting material