Sensitivity to ITD changes in a binaural detection model

In this contribution, we analyze the binaural model, proposed by Breebaart, van de Par and Kohlrausch in 2001, for its ability to predict just noticeable differences in interaural time differences (ITDs). This model is conceptually similar to crosscorrelation models, and the relevant model property for ITD detection is its internal delay line. We first study, which point along the internal delay axis changes most when the ITD of a sinusoidal stimulus changes. There are two candidate positions: First, the position where the crosscorrelation function of the reference stimulus has its maximum (e.g., zero ms for a stimulus without any ITD), and secondly a point at which the crosscorrelation function has its steepest slope, which is at a delay corresponding to a quarter period of the stimulus. With this analysis, we can also compare the model’s thresholds depending on the considered positions. A second question of interest is how the model deals with stimulus randomness in ITD experiments. From perception experiments it is known that the thresholds for sinusoidal stimuli and for narrowband random-noise stimuli with the same center frequency are very close

Rotational Brownian motion on the sphere surface and rotational relaxation

The spatial components of the autocorrelation function of noninteracting dipoles are analytically obtained in terms of rotational Brownian motion on the surface of a unit sphere using multi-level jumping formalism based on Debye's rotational relaxation model, and the rotational relaxation functions are evaluated.Comment: RevTex, 4 pages, submitted to Chin. Phys. Let

Towards ultra-high resolution 3D reconstruction of a whole rat brain from 3D-PLI data

3D reconstruction of the fiber connectivity of the rat brain at microscopic scale enables gaining detailed insight about the complex structural organization of the brain. We introduce a new method for registration and 3D reconstruction of high- and ultra-high resolution (64 $\mu$m and 1.3 $\mu$m pixel size) histological images of a Wistar rat brain acquired by 3D polarized light imaging (3D-PLI). Our method exploits multi-scale and multi-modal 3D-PLI data up to cellular resolution. We propose a new feature transform-based similarity measure and a weighted regularization scheme for accurate and robust non-rigid registration. To transform the 1.3 $\mu$m ultra-high resolution data to the reference blockface images a feature-based registration method followed by a non-rigid registration is proposed. Our approach has been successfully applied to 278 histological sections of a rat brain and the performance has been quantitatively evaluated using manually placed landmarks by an expert.Comment: 9 pages, Accepted at 2nd International Workshop on Connectomics in NeuroImaging (CNI), MICCAI'201

The Spin Glass Transition : Exponents and Dynamics

Numerical simulations on Ising Spin Glasses show that spin glass transitions do not obey the usual universality rules which hold at canonical second order transitions. On the other hand the dynamics at the approach to the transition appear to take up a universal form for all spin glasses. The implications for the fundamental physics of transitions in complex systems are addressed.Comment: 4 pages (Latex) with 3 figures (postscript), accepted for publication in Physica

Anomalous Rotational Relaxation: A Fractional Fokker-Planck Equation Approach

In this study we obtained analytically relaxation function in terms of rotational correlation functions based on Brownian motion for complex disordered systems in a stochastic framework. We found out that rotational relaxation function has a fractional form for complex disordered systems, which indicates relaxation has non-exponential character obeys to Kohlrausch-William-Watts law, following the Mittag-Leffler decay.Comment: Revtex4, 9 pages. Paper was revised. References adde

Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts

We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, non-harmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range $10^8 \div 10^9$ Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnetic by exciting the above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review

Correlation and response in the Backgammon model: the Ehrenfest legacy

We pursue our investigation of the non-equilibrium dynamics of the Backgammon model, a dynamical urn model which exhibits aging and glassy behavior at low temperature. We present an analytical study of the scaling behavior of the local correlation and response functions of the density fluctuations of the model, and of the associated fluctuation- dissipation ratios, throughout the alpha regime of low temperatures and long times. This analysis includes the aging regime, the convergence to equilibrium, sand the crossover behavior between them.Comment: 30 pages, 2 figures. To appear in Journal of Physics

Nonequilibrium dynamics of urn models

Dynamical urn models, such as the Ehrenfest model, have played an important role in the early days of statistical mechanics. Dynamical many-urn models generalize the former models in two respects: the number of urns is macroscopic, and thermal effects are included. These many-urn models are exactly solvable in the mean-field geometry. They allow analytical investigations of the characteristic features of nonequilibrium dynamics referred to as aging, including the scaling of correlation and response functions in the two-time plane and the violation of the fluctuation-dissipation theorem. This review paper contains a general presentation of these models, as well as a more detailed description of two dynamical urn models, the backgammon model and the zeta urn model.Comment: 15 pages. Contribution to the Proceedings of the ESF SPHINX meeting `Glassy behaviour of kinetically constrained models' (Barcelona, March 22-25, 2001). To appear in a special issue of J. Phys. Cond. Mat

A relaxation function encompassing the stretched exponential and the compressed hyperbola

A simple relaxation function I(t/tauzero; alpha, beta) unifying the stretched exponential with the compressed hyperbola is obtained, and its properties studied. The scaling parameter tauzero has dimensions of time, whereas the shape-determining parameters alpha and beta are dimensionless, both taking values between 0 and 1. For short times, the relaxation function is always exponential, with time constant tauzero. For small values of alpha, the function is close to exponential for all times, irrespective of beta. The function is also close to an exponential when beta is near unity, irrespective of alpha. For large values of alpha and long times, the function is close to a stretched exponential, provided that beta>0. The compressed hyperbola is recovered for beta=0.Comment: 17 pages, 4 figure

Stretched exponential relaxation in the mode-coupling theory for the Kardar-Parisi-Zhang equation

We study the mode-coupling theory for the Kardar-Parisi-Zhang equation in the strong-coupling regime, focusing on the long time properties. By a saddle point analysis of the mode-coupling equations, we derive exact results for the correlation function in the long time limit - a limit which is hard to study using simulations. The correlation function at wavevector k in dimension d is found to behave asymptotically at time t as C(k,t)\simeq 1/k^{d+4-2z} (Btk^z)^{\gamma/z} e^{-(Btk^z)^{1/z}}, with \gamma=(d-1)/2, A a determined constant and B a scale factor.Comment: RevTex, 4 pages, 1 figur