25 research outputs found
Indicator function and complex coding for mixed fractional factorial designs
In a general fractional factorial design, the -levels of a factor are
coded by the -th roots of the unity. This device allows a full
generalization to mixed-level designs of the theory of the polynomial indicator
function which has already been introduced for two level designs by Fontana and
the Authors (2000). the properties of orthogonal arrays and regular fractions
are discussed
Two polynomial representations of experimental design
In the context of algebraic statistics an experimental design is described by
a set of polynomials called the design ideal. This, in turn, is generated by
finite sets of polynomials. Two types of generating sets are mostly used in the
literature: Groebner bases and indicator functions. We briefly describe them
both, how they are used in the analysis and planning of a design and how to
switch between them. Examples include fractions of full factorial designs and
designs for mixture experiments.Comment: 13 page
Toric Statistical Models: Ising and Markov
This is a review of current research in Markov chains as toric statistical
models. Its content is mixture of background information, results from the
relevant recent literature, new results, and work in progress.Comment: 26 pages. Submitted Oct 10, 201
Cubature rules and expected value of some complex functions
The expected value of some complex valued random vectors is computed by means
of the indicator function of a designed experiment as known in algebraic statistics. The general
theory is set-up and results are obtained for nite discrete random vectors and the Gaussian random
vector. The precision space of some cubature rules/designed experiments are determined
Aberration in qualitative multilevel designs
Generalized Word Length Pattern (GWLP) is an important and widely-used tool
for comparing fractional factorial designs. We consider qualitative factors,
and we code their levels using the roots of the unity. We write the GWLP of a
fraction using the polynomial indicator function, whose
coefficients encode many properties of the fraction. We show that the
coefficient of a simple or interaction term can be written using the counts of
its levels. This apparently simple remark leads to major consequence, including
a convolution formula for the counts. We also show that the mean aberration of
a term over the permutation of its levels provides a connection with the
variance of the level counts. Moreover, using mean aberrations for symmetric
designs with prime, we derive a new formula for computing the GWLP of
. It is computationally easy, does not use complex numbers and
also provides a clear way to interpret the GWLP. As case studies, we consider
non-isomorphic orthogonal arrays that have the same GWLP. The different
distributions of the mean aberrations suggest that they could be used as a
further tool to discriminate between fractions.Comment: 16 pages, 1 figur
Differential effects of open- and closed-loop intracortical microstimulation on firing patterns of neurons in distant cortical areas
Intracortical microstimulation can be used successfully to modulate neuronal activity. Activity dependent stimulation (ADS), in which action potentials recorded extracellularly from a single neuron are used to trigger stimulation at another cortical location (closed-loop), is an effective treatment for behavioral recovery after brain lesion, but the related neurophysiological changes are still not clear. Here we investigated the ability of ADS and random stimulation (RS) to alter firing patterns of distant cortical locations. We recorded 591 neuronal units from 23 Long-Evan healthy anesthetized rats. Stimulation was delivered to either forelimb or barrel field somatosensory cortex, using either RS or ADS triggered from spikes recorded in the rostral forelimb area (RFA). Both RS and ADS stimulation protocols rapidly altered spike firing within RFA compared with no stimulation. We observed increase in firing rates and change of spike patterns. ADS was more effective than RS in increasing evoked spikes during the stimulation periods, by producing a reliable, progressive increase in stimulus-related activity over time and an increased coupling of the trigger channel with the network. These results are critical for understanding the efficacy of closed-loop electrical microstimulation protocols in altering activity patterns in interconnected brain networks, thus modulating cortical state and functional connectivity