30,814 research outputs found
Bayesian nonparametric tests via sliced inverse modeling
We study the problem of independence and conditional independence tests
between categorical covariates and a continuous response variable, which has an
immediate application in genetics. Instead of estimating the conditional
distribution of the response given values of covariates, we model the
conditional distribution of covariates given the discretized response (aka
"slices"). By assigning a prior probability to each possible discretization
scheme, we can compute efficiently a Bayes factor (BF)-statistic for the
independence (or conditional independence) test using a dynamic programming
algorithm. Asymptotic and finite-sample properties such as power and null
distribution of the BF statistic are studied, and a stepwise variable selection
method based on the BF statistic is further developed. We compare the BF
statistic with some existing classical methods and demonstrate its statistical
power through extensive simulation studies. We apply the proposed method to a
mouse genetics data set aiming to detect quantitative trait loci (QTLs) and
obtain promising results.Comment: 32 pages, 7 figure
Monte-Carlo Simulations of Spin-Crossover Phenomena Based on a Vibronic Ising-like Model with Realistic Parameters
Materials with spin-crossover (SCO) properties hold great potentials in
information storage and therefore have received a lot of concerns in the recent
decades. The hysteresis phenomena accompanying SCO is attributed to the
intermolecular cooperativity whose underlying mechanism may have a vibronic
origin. In this work, a new vibronic Ising-like model in which the elastic
coupling between SCO centers is included by considering harmonic stretching and
bending (SAB) interactions is proposed and solved by Monte Carlo simulations.
The key parameters in the new model, and , corresponding to the
elastic constant of the stretching and bending mode, respectively, can be
directly related to the macroscopic bulk and shear modulus of the material in
study, which can be readily estimated either based on experimental measurements
or first-principles calculations. The convergence issue in the MC simulations
of the thermal hysteresis has been carefully checked, and it was found that the
stable hysteresis loop can be more readily obtained when using the SAB model
compared to that using the Wajnflasz-Pick model. Using realistic parameters
estimated based on first-principles calculations of a specific polymeric
coordination SCO compound, [Fe(pz)Pt(CN)]2HO,
temperature-induced hysteresis and pressure effects on SCO phenomena are
simulated successfully.Comment: 8 pages, 8 figure
On the nonintegrability of equations for long- and short-wave interactions
We examine the integrability of two models used for the interaction of long
and short waves in dispersive media. One is more classical but arguably cannot
be derived from the underlying water wave equations, while the other one was
recently derived. We use the method of Zakharov and Schulman to attempt to
construct conserved quantities for these systems at different orders in the
magnitude of the solutions. The coupled KdV-NLS model is shown to be
nonintegrable, due to the presence of fourth-order resonances. A coupled real
KdV - complex KdV system is shown to suffer the same fate, except for three
special choices of the coefficients, where higher-order calculations or a
different approach are necessary to conclude integrability or the absence
thereof.Comment: 9 pages, presented as a poster at The Tenth IMACS International
Conference on Nonlinear Evolution Equations and Wave Phenomena: Computation
and Theor
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