37,718 research outputs found
Skew-symmetric distributions and Fisher information -- a tale of two densities
Skew-symmetric densities recently received much attention in the literature,
giving rise to increasingly general families of univariate and multivariate
skewed densities. Most of those families, however, suffer from the inferential
drawback of a potentially singular Fisher information in the vicinity of
symmetry. All existing results indicate that Gaussian densities (possibly after
restriction to some linear subspace) play a special and somewhat intriguing
role in that context. We dispel that widespread opinion by providing a full
characterization, in a general multivariate context, of the information
singularity phenomenon, highlighting its relation to a possible link between
symmetric kernels and skewing functions -- a link that can be interpreted as
the mismatch of two densities.Comment: Published in at http://dx.doi.org/10.3150/12-BEJ346 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
A general method for the statistical evaluation of typological distributions
The distribution of linguistic structures in the world is the joint product of universal principles, inheritance from ancestor languages, language contact, social structures, and random fluctuation. This paper proposes a method for evaluating the relative significance of each factor — and in particular, of universal principles — via regression modeling: statistical evidence for universal principles is found if the odds for families to have skewed responses (e.g. all or most members have postnominal relative clauses) as opposed to having an opposite response skewing or no skewing at all, is significantly higher for some condition (e.g. VO order) than for another condition, independently of other factors
Flexible modelling in statistics: past, present and future
In times where more and more data become available and where the data exhibit
rather complex structures (significant departure from symmetry, heavy or light
tails), flexible modelling has become an essential task for statisticians as
well as researchers and practitioners from domains such as economics, finance
or environmental sciences. This is reflected by the wealth of existing
proposals for flexible distributions; well-known examples are Azzalini's
skew-normal, Tukey's -and-, mixture and two-piece distributions, to cite
but these. My aim in the present paper is to provide an introduction to this
research field, intended to be useful both for novices and professionals of the
domain. After a description of the research stream itself, I will narrate the
gripping history of flexible modelling, starring emblematic heroes from the
past such as Edgeworth and Pearson, then depict three of the most used flexible
families of distributions, and finally provide an outlook on future flexible
modelling research by posing challenging open questions.Comment: 27 pages, 4 figure
Comparison of Induction and PM Synchronous motor drives for EV application including design examples
Three different motor drives for electric traction are compared, in terms of output power and efficiency at the same stack dimensions and inverter size. Induction motor (IM), surface-mounted permanent-magnet (PM) (SPM), and interior PM (IPM) synchronous motor drives are investigated, with reference to a common vehicle specification. The IM is penalized by the cage loss, but it is less expensive and inherently safe in case of inverter unwilled turnoff due to natural de-excitation. The SPM motor has a simple construction and shorter end connections, but it is penalized by eddy-current loss at high speed, has a very limited transient overload power, and has a high uncontrolled generator voltage. The IPM motor shows the better performance compromise, but it might be more complicated to be manufactured. Analytical relationships are first introduced and then validated on three example designs and finite element calculated, accounting for core saturation, harmonic losses, the effects of skewing, and operating temperature. The merits and limitations of the three solutions are quantified comprehensively and summarized by the calculation of the energy consumption over the standard New European Driving Cycl
A Constructive Representation of Univariate Skewed Distributions
We introduce a general perspective on the introduction of skewness into symmetric distributions. Making use of inverse probability integral transformations we provide a constructive representation of skewed distributions, where the skewing mechanism and the original symmetric distributions are specified separately. We study the effects of the skewing mechanism on \emph{e.g.} modality, tail behaviour and the amount of skewness generated. In light of the constructive representation, we review a number of characteristics of three classes of skew distributions previously defined in the literature. The representation is also used to introduce two novel classes of skewed distributions. Finally, we incorporate the different classes of distributions into a Bayesian linear regression framework and analyse their differences and similarities.Arnold and Groeneveld skewness measure, Bayesian regression model, inverse probability integral transformation, modality, skewing mechanism, tail behaviour
Skewed Parton Distributions and F_2^D at beta -> 1
We show that the diffractive structure function is perturbatively calculable
in the domain where the diffractive mass is small but still outside the
resonance region. In this domain, which can be characterized by Lambda^2/Q^2 <<
1-beta << (Lambda^2/Q^2)^1/2, the structure function represents a new
observable, which is highly sensitive to the small-x skewed gluon distribution.
Our leading order calculation and the estimate of next-to-leading order
corrections are consistent with available data and demonstrate the potential of
more precise data to put further constraints on skewing effects.Comment: 11 pages, LaTeX, including five PostScript figure
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