265 research outputs found
The Independent Sign Bias: Gaining Insight from Multiple Linear Regression
No full textAs electronic data becomes widely available, the need for tools that help people gain insight from data has arisen. A variety of techniques from statistics, machine learning, and neural networks have been applied to databases in the hopes of mining knowledge
from data. Multiple regression is one such method for modeling the relationship between a set of explanatory variables and a dependent variable by fitting a linear equation to observed data. Here, we investigate and discuss some factors that influence whether the resulting regression equation is a credible model of the
data.Pazzani, Michael J. and Bay, Stephen D. (1999). "The Indepdendent Sign Bias: Gaining Insight from Multiple Linear Regression" Proceedings of the Twenty First Annual Conference of the Cognitive Science Society.This research was funded in part by the National Science
Foundation grant IRI-9713990
Susceptibility to rifaximin of Vibrio cholerae strains from different geographical areas
No full textFour hundred and eight clinical strains of Vibrio cholerae isolated from different geographical areas and with different antimicrobial resistance patterns were tested for susceptibility to rifaximin, a non-absorbable antibiotic active in vitro against Gram-negative bacteria. The MICs ranged from 0.5 to 4 mg/l for all strains. These values and the pharmacokinetic properties suggest rifaximin as an attractive antimicrobial agent for choler
Traps and pitfalls when learning logical definitions from relations
No full textIn the paper, we present some learning tasks that cannot be solved by two wellknown systems, FOIL and FOCL. Two kinds of explanations can be provided for these failures. For some tasks, the failures can be ascribed to a wrong definition of the space in which these systems perform the search for logical definitions. By moving from θ-subsumption to a weaker, but more mechanizable and manageable, model of generalization, called θOI-subsumption, a new search space is defined in which such tasks can be solved. Such a solution has been implemented in a new version of FOCL, called FOCL-OI. However, other learning tasks cannot be solved by changing the search space. For these tasks, the conceptual problem detected both in FOIL and in FOCL concerns the generation of meaningless rules, which do not mirror at all the structure of the training instances. We claim that, whenever possible, the training/test examples should be represented as ground Horn clauses, rather than as tuples of a relational database or facts of a Prolog database
Avoiding Non-termination when Learning Logical Programs: A Case Study with FOIL and FOCL
No full textMany systems that learn logic programs from examples adopt θ-subsumption as model of generalization and refer to Plotkin's framework in order to define their search space. However, they seldom take into account the fact that the lattice defined by Plotkin is a set of equivalence classes rather than simple clauses. This may lead to non-terminating learning processes, since the search gets stuck within an equivalence class, which contains an infinite number of clauses.
In the paper, we present a task that cannot be solved by two well-known systems that learn logic programs, FOIL and FOCL. The failure is explained on the ground of the previous consideration about the search space. This task can be solved by adopting a weaker, but more mechanizable and manageable, model of generalization, called θ-subsumption under object identity (θ OI-subsumption). Such a solution has been implemented in a new version of FOCL, called FOCL-OI
Antimicrobial resistance gene shuffling and a three-element mobilisation system in the monophasic Salmonella typhimurium strain ST1030
No full textIn this study we describe the genetic elements and the antimicrobial resistance units (RUs) harboured by the Salmonella Typhimurium monophasic variant 1,4,[5],12:i:- strain ST1030. Of the three identified RUs two were chromosomal, RU1 (IS26-blaTEM-1-IS26-strAB-sul2- IS26) and RU2 (IS26-tetR(B)-tetA(B)-ΔIS26), and one, RU3 (a sul3-associated class 1 integron with cassette array dfrA12-orfF-aadA2-cmlA1-aadA1), was embedded in a Tn21-derived element harboured by the conjugative I1 plasmid pST1030-1A. IS26 elements mediated the antimicrobial resistance gene (ARG) shuffling and this gave rise to pST1030-1A derivatives with different sets of ARGs. ST1030 also harboured two ColE1-like plasmids of which one, pST1030-2A, was mobilisable and the target of an intracellular translocation of the Tn21-derived element; the second (pST1030-3) was an orphan mob-associated oriT plasmid co-transferred with pST1030-1A and pST1030-2A. pST1030-2A and pST1030-3 also carried a parA gene and a type III restriction modification system, respectively. Overall analysis of our data reinforces the role played by IS26, Tn21-derived elements and non-conjugative plasmids in the spread of ARGs and supplies the first evidence, at least in Salmonella, for the identification of a natural isolate harbouring a three-element mobilisation system in the same cell
Characterization of endemic Shigella flexneri strains in Somalia: antimicrobial resistance, plasmid profiles, and serotype correlation
No full textOn the Role of Low-Mass Asymptotic Giant Branch Stars in Producing a Solar System Distribution of s-Process Isotopes
No full textThe production of s-isotopes due to the operation of the reaction 13C(α, n)16O in low-mass stars during asymptotic giant branch phases is investigated following in detail the time evolution of the thermal pulses, the temperature and density stratification within the convective shells, and taking into account the effect of the neutron recycling by 12C through the chain 12C(n, γ)13C(α, n)16O. The resulting average neutron density reaches a maximum of about 5×109cm-3 and then decreases smoothly. Strong overabundances for all s-isotopes with A > 80 are obtained in a solar system distribution. The process appears suitable to reproduce many observed details concerning isotopic ratios
Variability of Point Mutation Rates in Campylobacter coli: Preliminary Data and Observations.
No full textIn this study we evaluated the in vitro variability of flaA in Campylobacter coli
strains (Co19 and Co29) isolated from distinct poultry farms. Strains were
characterized by flaA PCR-RFLP and subcultured in absence or presence of
Salmonella enterica (S. Gallinarum) as a host competitor in poultry. Only transition
mutations were detected and no flaA-flaB recombination events were observed. The
highest ratio of flaA mutations was detected in the presence of competitor (1x10-6
and 4.8x10-6 for Co19 and Co29, respectively). While, transitions in absence of
competitor were observed only in the strain Co29 (5.8x10-7). Data obtained in this
investigation represent a preliminary study aimed to evaluate the possible linkage between specific haplotypes and their proneness to acquire point mutations which in turn might help strains to gain a better fitness for survival within and outside hosts
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