318,346 research outputs found
The generalized localization lengths in one dimensional systems with correlated disorder
The scale invariant properties of wave functions in finite samples of one
dimensional random systems with correlated disorder are analyzed. The random
dimer model and its generalizations are considered and the wave functions are
compared. Generalized entropic localization lengths are introduced in order to
characterize the states and compared with their behavior for exponential
localization. An acceptable agreement is obtained, however, the exponential
form seems to be an oversimplification in the presence of correlated disorder.
According to our analysis in the case of the random dimer model and the two new
models the presence of power-law localization cannot be ruled out.Comment: 7 pages, LaTeX (IOP style), 2 figure
The F\"ollmer-Schweizer decomposition under incomplete information
In this paper we study the F\"ollmer-Schweizer decomposition of a square
integrable random variable with respect to a given semimartingale
under restricted information. Thanks to the relationship between this
decomposition and that of the projection of with respect to the given
information flow, we characterize the integrand appearing in the
F\"ollmer-Schweizer decomposition under partial information in the general case
where is not necessarily adapted to the available information level. For
partially observable Markovian models where the dynamics of depends on an
unobservable stochastic factor , we show how to compute the decomposition by
means of filtering problems involving functions defined on an
infinite-dimensional space. Moreover, in the case of a partially observed
jump-diffusion model where is described by a pure jump process taking
values in a finite dimensional space, we compute explicitly the integrand in
the F\"ollmer-Schweizer decomposition by working with finite dimensional
filters.Comment: 22 page
ESTIMATES COVARIANCE FUNCTIONS TO GOATS MILK PRODUCTION USING REGRESSION MODELS RANDOM
The aim of this review was to estimate covariance functions for the production of Alpine breeds of goat milk and Saanen using random regression models. Conventional analysis for estimating components of (co) variance and genetic parameters for growth traits are performed by finite-dimensional models, which allows the construction and use of selection indexes and mixed model equations, obtaining parameters as heritability and genetic correlation. The random regression models (MRA) enable work with characteristics of genetic lactation curves for each animal or growth that are measured repeatedly in the animal's life, called longitudinal data
Efficient High-Dimensional Importance Sampling
The paper describes a simple, generic and yet highly accurate Efficient Importance Sampling (EIS) Monte Carlo (MC) procedure for the evaluation of high-dimensional numerical integrals. EIS is based upon a sequence of auxiliary weighted regressions which actually are linear under appropriate conditions. It can be used to evaluate likelihood functions and byproducts thereof, such as ML estimators, for models which depend upon unobservable variables. A dynamic stochastic volatility model and a logit panel data model with unobserved heterogeneity (random effects) in both dimensions are used to provide illustrations of EIS high numerical accuracy, even under small number of MC draws. MC simulations are used to characterize the finite sample numerical and statistical properties of EIS-based ML estimators.
Discretization of Random Fields Representing Material Properties and Distributed Loads in FORM Analysis
The reliability analysis of more complicated structures usually deals with the finite element method (FEM) models. The random fields (material properties and loads) have to be represented by random variables assigned to random field elements. The adequate distribution functions and covariance matrices should be determined for a chosen set of random variables. This procedure is called discretization of a random field. The chapter presents the discretization of random field for material properties with the help of the spatial averaging method of one-dimensional homogeneous random field and midpoint method of discretization of random field. The second part of the chapter deals with the discretization of random fields representing distributed loads. In particular, the discretization of distributed load imposed on a Bernoulli beam is presented in detail. Numerical example demonstrates very good agreement of the reliability indices computed with the help of stochastic finite element method (SFEM) and first-order reliability method (FORM) analyses with the results obtained from analytical formulae
Free-energy distribution functions for the randomly forced directed polymer
We study the -dimensional random directed polymer problem, i.e., an
elastic string subject to a Gaussian random potential and
confined within a plane. We mainly concentrate on the short-scale and
finite-temperature behavior of this problem described by a short- but
finite-ranged disorder correlator and introduce two types of
approximations amenable to exact solutions. Expanding the disorder potential
at short distances, we study the
random force (or Larkin) problem with as well as the shifted
random force problem including the random offset ; as such, these
models remain well defined at all scales. Alternatively, we analyze the
harmonic approximation to the correlator in a consistent manner.
Using direct averaging as well as the replica technique, we derive the
distribution functions and of free energies
of a polymer of length for both fixed () and free boundary
conditions on the displacement field and determine the mean
displacement correlators on the distance . The inconsistencies encountered
in the analysis of the harmonic approximation to the correlator are traced back
to its non-spectral correlator; we discuss how to implement this approximation
in a proper way and present a general criterion for physically admissible
disorder correlators .Comment: 16 pages, 5 figure
Stochastic attractors for shell phenomenological models of turbulence
Recently, it has been proposed that the Navier-Stokes equations and a
relevant linear advection model have the same long-time statistical properties,
in particular, they have the same scaling exponents of their structure
functions. This assertion has been investigate rigorously in the context of
certain nonlinear deterministic phenomenological shell model, the Sabra shell
model, of turbulence and its corresponding linear advection counterpart model.
This relationship has been established through a "homotopy-like" coefficient
which bridges continuously between the two systems. That is, for
one obtains the full nonlinear model, and the corresponding linear
advection model is achieved for . In this paper, we investigate the
validity of this assertion for certain stochastic phenomenological shell models
of turbulence driven by an additive noise. We prove the continuous dependence
of the solutions with respect to the parameter . Moreover, we show the
existence of a finite-dimensional random attractor for each value of
and establish the upper semicontinuity property of this random attractors, with
respect to the parameter . This property is proved by a pathwise
argument. Our study aims toward the development of basic results and techniques
that may contribute to the understanding of the relation between the long-time
statistical properties of the nonlinear and linear models
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