Search results for "statistical [methods]"
showing 10 items of 1664 documents
A wideband car-to-car channel model based on a geometrical semicircular tunnel scattering model
2013
In this paper, we present a wideband single-input single-output (SISO) car-to-car (C2C) channel model based on a geometrical semicircular tunnel (SCT) scattering model. Starting from the geometrical scattering model, a reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. In the proposed channel model, it is assumed that an infinite number of scatterers are uniformly distributed on the tunnel wall. Starting from the geometrical scattering model, the time-variant transfer function (TVTF) is derived and its correlation properties are studied. Expressions are presented for the two-dimensional (2D)…
<title>Correlation effects in the disordered ferroelectrics</title>
2003
ABSTRACT The calculation of the correlation radius distribution function is performed for the cases of undamped and overdamped softmode dispersion laws. Taking into account the correlation radius dependence on the random field and this field distribution function we carried out the theoretical calculation of the correlation radius distribution function dependence ontemperature, damping coefficient and random field distribution function parameters. It was shown that at temperaturehigher than Burns temperature Td the most probable value of the correlation radius is equal to its maximal valueindependently on the system disorder, while in the dipole glass state it is close to the minimal value …
Surface-directed spinodal decomposition in a thin-film geometry: A computer simulation
1994
The phase separation kinetics of a two-dimensional binary mixture at critical composition confined between (one-dimensional) straight walls which preferentially attract one component of the mixture is studied for a wide range of distancesD between the walls. Following earlier related work on semiinfinite systems, two choices of surface forces at the walls are considered, one corresponding to an incompletely wet state of the walls, the other to a completely wet state (forD→∞). The nonlinear Cahn-Hilliard-type equation, supplemented with appropriate boundary conditions which account for the presence of surfaces, is replaced by a discrete equivalent and integrated numerically. Starting from a …
Reconstruction of random media using Monte Carlo methods.
1998
A simulated annealing algorithm is applied to the reconstruction of two-dimensional porous media with prescribed correlation functions. The experimental correlation function of an isotropic sample of Fontainebleau sandstone and a synthetic correlation function with damped oscillations are used in the reconstructions. To reduce the numerical effort we follow a proposal suggesting the evaluation of the correlation functions only along certain directions. The results show that this simplification yields significantly different microstructures as compared to a full evaluation of the correlation function. In particular, we find that the simplified reconstruction method introduces an artificial a…
Monte Carlo estimation of transverse and longitudinal correlation functions in the model
2010
Abstract Monte Carlo simulations of the three-dimensional O ( 4 ) model in the ordered phase are performed to study the Goldstone mode effects. Our data show a distinct scaling region, where the Fourier-transformed transverse correlation function behaves as ∝ k − λ ⊥ with λ ⊥ 2 ( λ ≃ 1.95 ), in disagreement with the standard theoretical prediction λ ⊥ = 2 .
The ALHAMBRA survey: Estimation of the clustering signal encoded in the cosmic variance
2015
[Aims]: The relative cosmic variance (σv) is a fundamental source of uncertainty in pencil-beam surveys and, as a particular case of count-in-cell statistics, can be used to estimate the bias between galaxies and their underlying dark-matter distribution. Our goal is to test the significance of the clustering information encoded in the σv measured in the ALHAMBRA survey. [Methods]: We measure the cosmic variance of several galaxy populations selected with B-band luminosity at 0.35 ≤ z< 1.05 as the intrinsic dispersion in the number density distribution derived from the 48 ALHAMBRA subfields. We compare the observational σv with the cosmic variance of the dark matter expected from the theory…
Morphostatistical characterization of the spatial galaxy distribution through Gibbs point processes
2021
This paper proposes a morpho-statistical characterisation of the galaxy distribution through spatial statistical modelling based on inhomogeneous Gibbs point processes. The galaxy distribution is supposed to exhibit two components. The first one is related to the major geometrical features exhibited by the observed galaxy field, here, its corresponding filamentary pattern. The second one is related to the interactions exhibited by the galaxies. Gibbs point processes are statistical models able to integrate these two aspects in a probability density, controlled by some parameters. Several such models are fitted to real observational data via the ABC Shadow algorithm. This algorithm provides …
Effect of physical activity counseling on physical activity of older people in Finland (ISRCTN 07330512).
2011
SUMMARY The aim of this study was to describe the underlying theory and the implementation of a 2-year individualized physical activity counseling intervention and to evaluate whether benefits persisted 1.5 years after the intervention. The sample included 632 sedentary 75- to 81-year-old participants. Data were collected in 2003 –2005. The participants were randomly assigned to an intervention group and a control group. The intervention consisted of an individualized face-to-face meeting followed by telephone contacts every 4 months for 2 years, with the aim to increase participation in specific physical activities as well as to increase habitual physical activity. At the 2-year follow-up,…
Pattern formation and spatial correlation induced by the noise in two competing species
2004
We analyze the spatio-temporal patterns of two competing species in the presence of two white noise sources: an additive noise acting on the interaction parameter and a multiplicative noise which affects directly the dynamics of the species densities. We use a coupled map lattice (CML) with uniform initial conditions. We find a nonmonotonic behavior both of the pattern formation and the density correlation as a function of the multiplicative noise intensity.
Nonmonotonic behavior of spatiotemporal pattern formation in a noisy Lotka-Volterra system
2004
The noise-induced pattern formation in a population dynamical model of three interacting species in the coexistence regime is investigated. A coupled map lattice of Lotka-Volterra equations in the presence of multiplicative noise is used to analyze the spatiotemporal evolution. The spatial correlation of the species concentration as a function of time and of the noise intensity is investigated. A nonmonotonic behavior of the area of the patterns as a function of both noise intensity and evolution time is found.