Time-Reversal Methods in Acousto-Elastodynamics
The aim of the article is to solve an inverse problem in order to determine the presence and some properties of an elastic “inclusion” (an unknown object, characterized by elastic properties discriminant from the surrounding medium) from partial observations of acoustic waves, scattered by the inclusion. The method will require developing techniques based on Time Reversal methods. A finite element method based on acousto-elastodynamics equations will be derived and used to solve the inverse problem. Our approach will be applied to configurations modeling breast cancer detection, using simulated ultrasound waves.
In this paper we study the performance of IEEE 802.11e enhanced distributed channel access (EDCA) priority schemes under finite load and error-prone channel. We introduce a multi-dimensional Markov Chain model that includes all the mandatory differentiation mechanisms of the standard: QoS parameters, CWMIN, CWMAX arbitration inter-frame space (AIFS), and the virtual collision handler. The model faithfully represents the functionality of the EDCA access mechanisms, including lesser known details of the standard such as the management of the backoff counter which is technically different from the one used in the legacy DCF. We study the priority schemes under both finite load and saturation conditions. Our analysis also takes into consideration channel conditions.