Spatial repeatability of dynamic tyre forces generated by heavy vehicles

Road damage due to heavy vehicles is thought to be dependent on the extent to which lorries in normal traffic apply peak forces to the same locations along the road. A validated vehicle simulation is used to simulate 37 leaf-sprung articulated vehicles with parametric variations typical of vehicles in one weight class in the highway vehicle fleet. The spatial distribution of tyre forces generated by each vehicle is compared with the distribution generated by a reference vehicle, and the conditions are established for which repeated heavy loading occurs at specific points along the road. It is estimated that approximately two-thirds of vehicles in this class (a large proportion of all heavy vehicles) may contribute to a repeated pattern of road loading. It is concluded that dynamic tyre forces are a significant factor influencing road damage, compared to other factors such as tyre configuration and axle spacing.

Three-dimensional distribution of Al in high-k metal gate: Impact on transistor voltage threshold

The three-dimensional spatial distribution of Al in the high-k metal gates of metal-oxide-semiconductor field-effect-transistors is measured by atom probe tomography. Chemical distribution is correlated with the transistor voltage threshold (VTH) shift generated by the introduction of a metallic Al layer in the metal gate. After a 1050 °C annealing, it is shown that a 2-Å thick Al layer completely diffuses into oxide layers, while a positive VTH shift is measured. On the contrary, for thicker Al layers, Al precipitation in the metal gate stack is observed and the VTH shift becomes negative. © 2012 American Institute of Physics.

On the applicability of the lognormal distribution in random dynamical systems

This paper is concerned with the probability density function of the energy of a random dynamical system subjected to harmonic excitation. It is shown that if the natural frequencies and mode shapes of the system conform to the Gaussian Orthogonal Ensemble, then under common types of loading the distribution of the energy of the response is approximately lognormal, providing the modal overlap factor is high (typically greater than two). In contrast, it is shown that the response of a system with Poisson natural frequencies is not approximately lognormal. Numerical simulations are conducted on a plate system to validate the theoretical findings and good agreement is obtained. Simulations are also conducted on a system made from two plates connected with rotational springs to demonstrate that the theoretical findings can be extended to a built-up system. The work provides a theoretical justification of the commonly used empirical practice of assuming that the energy response of a random system is lognormal.