1,418 research outputs found
Learning When Training Data are Costly: The Effect of Class Distribution on Tree Induction
For large, real-world inductive learning problems, the number of training
examples often must be limited due to the costs associated with procuring,
preparing, and storing the training examples and/or the computational costs
associated with learning from them. In such circumstances, one question of
practical importance is: if only n training examples can be selected, in what
proportion should the classes be represented? In this article we help to answer
this question by analyzing, for a fixed training-set size, the relationship
between the class distribution of the training data and the performance of
classification trees induced from these data. We study twenty-six data sets
and, for each, determine the best class distribution for learning. The
naturally occurring class distribution is shown to generally perform well when
classifier performance is evaluated using undifferentiated error rate (0/1
loss). However, when the area under the ROC curve is used to evaluate
classifier performance, a balanced distribution is shown to perform well. Since
neither of these choices for class distribution always generates the
best-performing classifier, we introduce a budget-sensitive progressive
sampling algorithm for selecting training examples based on the class
associated with each example. An empirical analysis of this algorithm shows
that the class distribution of the resulting training set yields classifiers
with good (nearly-optimal) classification performance
Asteroseismology and calibration of alpha Cen binary system
Using the oscillation frequencies of alpha Cen A recently discovered by
Bouchy & Carrier, the available astrometric, photometric and spectroscopic
data, we tried to improve the calibration of the visual binary system alpha
Cen. With the revisited masses of Pourbaix et al. (2002) we do not succeed to
obtain a solution satisfying all the seismic observational constraints.
Relaxing the constraints on the masses, we have found an age t_alpha
Cen=4850+-500 Myr, an initial helium mass fraction Y_i = 0.300+-0.008, and an
initial metallicity (Z/X)_i=0.0459+-0.0019, with M_A=1.100+-0.006M_o and
M_B=0.907+-0.006M_o for alpha Cen A&B.Comment: accepted for publication as a letter in A&
Calibrations of alpha Cen A & B
Detailed evolutionary models of the visual binary alpha Centauri, including
pre main-sequence evolution, have been performed using the masses recently
determined by Pourbaix et al. (1999). Models have been constructed using the
CEFF equation of state, OPAL opacities, NACRE thermonuclear reaction rates and
microscopic diffusion. A chi^2-minimization is performed to derive the most
reliable set of modeling parameters wp={t_alpha Cen, Yi, [Fe/H]i, alpha A,
alpha B}, where t alpha Cen is the age of the system, Yi the initial helium
content, [Fe/H]i the initial metallicity and, alpha A and alpha B the
convection parameters of the two components. Using the basic Bohm-Vitense
(1958) mixing-length theory of convection, we derive wp BV={2710 Myr,
0.284,0.257, 1.53, 1.57}. We obtain a noticeably smaller age than estimated
previously, in agreement with Pourbaix et al. (1999), mainly because of the
larger masses. If convective core overshoot is considered we get wp ov={3530
Myr, 0.279,0.264,1.64,1.66}. The use of Canuto & Mazitelli (1991, 1992)
convection theory leads to the set wp CM={4086 Myr, 0.271, 0.264, 0.964,
0.986}. Using the observational constraints adopted by Guenther & Demarque
(2000), and the basic mixing-length theory, we obtain wp GD={5640 Myr, 0.300,
0.296, 1.86, 1.97} and surface lithium depletions close to their observed
values.
A seismological analysis of our calibrated models has been performed. The
determination of large and small spacings between the frequencies of acoustic
oscillations from seismic observations would help to discriminate between the
models of alpha Cen computed with different masses and to confirm or rules out
the new determination of masses.Comment: accepted for publication by A&
On Objective Measures of Rule Surprisingness
Most of the literature argues that surprisingness is an inherently subjective aspect of the discovered knowledge, which cannot be measured in objective terms. This paper departs from this view, and it has a twofold goal: (1) showing that it is indeed possible to define objective (rather than subjective) measures of discovered rule surprisingness; (2) proposing new ideas and methods for defining objective rule surprisingness measures
Ensembles of probability estimation trees for customer churn prediction
Customer churn prediction is one of the most, important elements tents of a company's Customer Relationship Management, (CRM) strategy In tins study, two strategies are investigated to increase the lift. performance of ensemble classification models, i.e (1) using probability estimation trees (PETs) instead of standard decision trees as base classifiers; and (n) implementing alternative fusion rules based on lift weights lot the combination of ensemble member's outputs Experiments ale conducted lot font popular ensemble strategics on five real-life chin n data sets In general, the results demonstrate how lift performance can be substantially improved by using alternative base classifiers and fusion tides However: the effect vanes lot the (Idol cut ensemble strategies lit particular, the results indicate an increase of lift performance of (1) Bagging by implementing C4 4 base classifiets. (n) the Random Subspace Method (RSM) by using lift-weighted fusion rules, and (in) AdaBoost, by implementing both
Neonatal Lupus Erythematosus: New Serologic Findings
A child with neonatal lupus was evaluated and found to possess serum anti Ro(SSA) antibodies. The cutaneous lesions and anti Ro(SSA) antibodies disappeared during the next 5 mo.The infant's mother was asymptomatic but possessed anti Ro(SSA) and anti La(SSB) antibodies
VINCI / VLTI observations of Main Sequence stars
Main Sequence (MS) stars are by far the most numerous class in the Universe.
They are often somewhat neglected as they are relatively quiet objects (but
exceptions exist), though they bear testimony of the past and future of our
Sun. An important characteristic of the MS stars, particularly the solar-type
ones, is that they host the large majority of the known extrasolar planets.
Moreover, at the bottom of the MS, the red M dwarfs pave the way to
understanding the physics of brown dwarfs and giant planets. We have measured
very precise angular diameters from recent VINCI/VLTI interferometric
observations of a number of MS stars in the K band, with spectral types between
A1V and M5.5V. They already cover a wide range of effective temperatures and
radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as
well as the asteroseismic information available for some of these stars, the
angular diameters put strong constraints on the detailed models of these stars,
and therefore on the physical processes at play.Comment: 5 pages, 3 figures. To appear in the Proceedings of IAU Symposium
219, "Stars as Suns", Editors A. Benz & A. Dupree, Astronomical Society of
the Pacifi
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