The Coulomb gap and low energy statistics for Coulomb glasses
We study the statistics of local energy minima in the configuration space of two-dimensional lattice Coulomb glasses with site disorder and the behavior of the Coulomb gap depending on the strength of random site energies. At intermediate disorder, i.e., when the typical strength of the disorder is of the same order as the nearest-neighbor Coulomb energy, the high energy tail of the distribution of the local minima is exponential. We furthermore analyze the structure of the local minima and show that most sites of the system have the same occupation numbers in all of these states. The density of states (DOS) shows a transition from the crystalline state at zero disorder (with a hard gap) to an intermediate, probably glassy state with a Coulomb gap. We analyze this Coulomb gap in some detail and show that the DOS deviates slightly from the traditional linear behavior in 2D. For finite systems these intermediate Coulomb gap states disappear for large disorder strengths and only a random localized state in which all electrons are in the minima of the random potential exists. Dedication: This paper is dedicated to Thomas Nattermann, our dearest friend, brilliant colleague, and outstanding teacher.
Slow relaxation and equilibrium dynamics in a two-dimensional Coulomb glass : Demonstration of stretched exponential energy correlations
We have simulated energy relaxation and equilibrium dynamics in Coulomb glasses using the random energy lattice model. We show that in a temperature range where the Coulomb gap is already well developed T = 0.03– 0.1, the system still relaxes to an equilibrium behavior within the simulation time scale. For all temperatures T, the relaxation is slower than exponential. Analyzing the energy correlations of the system at equilibrium C, we find a stretched exponential behavior, C =e � /0 . We study the temperature dependence of 0 and . 0 is shown to increase faster than exponentially with decreasing T. is proportional to T at low temperature and approaches unity for high temperature. We define a time from these stretched exponential correlations and show that this time corresponds well with the time required to reach equilibrium. From our data it is not possible to determine whether diverges at any finite temperature, indicating a glass transition, or whether this divergence happens at zero temperature. While the time dependence of the system energy can be well fitted by a random walker in a harmonic potential for high temperatures T =1 0, this simple model fails to describe the long time scales observed at lower temperatures. Instead we present an interpretation of the configuration space as a structure with fractal properties and the time evolution as a random walk on this fractal-like structure.
Application of infrared camera to bituminous concrete pavements: measuring vehicle
Infrared thermography (IR) has been used for decades in certain fields. However, the technological level of advancement of measuring devices has not been sufficient for some applications. Over the recent years, good quality thermal cameras with high resolution and very high thermal sensitivity have started to appear on the market. The development in the field of measuring technologies allowed the use of infrared thermography in new fields and for larger number of users. This article describes the research in progress in Transport Research Centre with a focus on the use of infrared thermography for diagnostics of bituminous road pavements. A measuring vehicle, equipped with a thermal camera, digital camera and GPS sensor, was designed for the diagnostics of pavements. New, highly sensitive, thermal cameras allow to measure very small temperature differences from the moving vehicle. This study shows the potential of a high-speed inspection without lane closures while using IR thermography.