Search results for "Random field"
showing 10 items of 78 documents
Unified Analysis of Periodization-Based Sampling Methods for Matérn Covariances
2020
The periodization of a stationary Gaussian random field on a sufficiently large torus comprising the spatial domain of interest is the basis of various efficient computational methods, such as the ...
Percolation and Schramm–Loewner evolution in the 2D random-field Ising model
2011
Abstract The presence of random fields is well known to destroy ferromagnetic order in Ising systems in two dimensions. When the system is placed in a sufficiently strong external field, however, the size of clusters of like spins diverges. There is evidence that this percolation transition is in the universality class of standard site percolation. It has been claimed that, for small disorder, a similar percolation phenomenon also occurs in zero external field. Using exact algorithms, we study ground states of large samples and find little evidence for a transition at zero external field. Nevertheless, for sufficiently small random-field strengths, there is an extended region of the phase d…
The physical mechanisms of relaxation times distribution in inorganic and organic disordered ferroelectrics
2007
Abstract We discuss the physical background for relaxation times distribution in organic and inorganic disordered ferroelectrics. We show that such background is a disorder which is believed to be a reason for relaxor behavior. Due to this disorder the internal electric and elastic fields are of a random nature being characterized by certain distribution function. Having the distribution function f ( E ) of random field E , we can obtain the distribution function of relaxation times F ( τ ) with the help of relation between τ and E . Latter relation can be obtained considering the dynamics of a single electric dipole in a random field created by the ensemble of defects and impurities in a s…
Observation of random-field behavior in (CO)1−x(N2)xmixtures physisorbed on graphite
1993
Heat-capacity studies have been carried out on submonolayers of (CO${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{N}}_{2}$${)}_{\mathit{x}}$ mixtures physisorbed on graphite. We find that pure CO undergoes an end-to-end ordering transition at ${\mathit{T}}_{\mathit{c}}$=5.18 K, which is shown to belong to the two-dimensional Ising universality class. In diluting CO with ${\mathrm{N}}_{2}$ the heat-capacity peaks become progressively rounded until the phase transition is completely suppressed at a ${\mathrm{N}}_{2}$ concentration of only x=0.07. The analysis of the data shows that this behavior is in quantitative agreement with predictions of the random-field theory applied to adsorbed…
Copolymer Melts in Disordered Media
1996
The symmetric AB block copolymer melt in a gel matrix with preferential adsorption of A monomers on the gel gives an example of a random-field system, which is described near the point of the microphase separation transition by the random field Landau-Brazovskii Hamiltonian. By using the technique of the 2-nd Legendre transform, the phase diagram of the system is calculated. We found that the preferential adsorption of the copolymer on the gel results in two effects: a) It decreases the temperature of the first order phase transition between disordered and ordered phase. b) There exists a region on the phase diagram at some small but finite value of the adsorption energy in which the replic…
On the theory of thermodynamic properties of geometrically confined disordered ferroelectrics
2013
Abstract We propose a theoretical approach to calculate the thermodynamic properties of thin films fabricated from disordered ferroelectrics. To calculate the above thermodynamic properties, we use so-called random field method, modified for the case of thin films. The essence of modification is the altering of the interaction between impurity dipoles by geometrical confinement. We show that in thin films the ferroelectric phase transition is inhibited as compared to the case of bulk samples. Our theory is generalizable to ferroelectrics of other shapes as well as magnets and multiferroics.
Modeling dark photon oscillations in our inhomogeneous Universe
2020
A dark photon may kinetically mix with the Standard Model photon, leading to observable cosmological signatures. The mixing is resonantly enhanced when the dark photon mass matches the primordial plasma frequency, which depends sensitively on the underlying spatial distribution of electrons. Crucially, inhomogeneities in this distribution can have a significant impact on the nature of resonant conversions. We develop and describe, for the first time, a general analytic formalism to treat resonant oscillations in the presence of inhomogeneities. Our formalism follows from the theory of level crossings of random fields and only requires knowledge of the one-point probability distribution func…
External noise effects on the electron velocity fluctuations in semiconductors
2008
We investigate the modification of the intrinsic carrier noise spectral density induced in low-doped semiconductor materials by an external correlated noise source added to the driving high-frequency periodic electric field. A Monte Carlo approach is adopted to numerically solve the transport equation by considering all the possible scattering phenomena of the hot electrons in the medium. We show that the noise spectra are strongly affected by the intensity and the correlation time of the external random electric field. Moreover this random field can cause a suppression of the total noise power.
Nucleosynthesis constraints on active-sterile neutrino conversions in the early universe with random magnetic field
1994
We consider active-sterile neutrino conversions in the early universe hot plasma in the presence of a random magnetic field generated at the electroweak phase transition. Within a random field domain the magnetization asymmetry of the lepton antilepton plasma produced by a uniform constant magnetic field is huge in contrast to their small density asymmetry, leading to a drastic change in the active-sterile conversion rates. Assuming that the random field provides the seed for the galactic field one can estimate the restrictions from primordial nucleosynthesis. Requiring that the extra sterile \neu does not enter in equilibrium with the active ones before nucleosynthesis we find limits of th…
First Versus Second Order Phase Transitions in the Three-Dimensional Three-State Potts Model in Random Fields
1995
The ordering of three-states Potts ferromagnets on the simple cubic lattice exposed to random fields is investigated by extensive Monte Carlo simulations. Evidence is presented that the transition is second order for intermediate strength of the fields, while it presumably is first order for large field strength. The implications for various theoretical predictions are briefly discussed.