Cerebral ischaemia and its relation to epilepsy.

During many years a number of observers have presented evidence suggesting that cerebral ischaemia, resulting from local vascular spasm, or from suddenly diminished blood supply to the brain as a whole, may be instrumental in producing an epileptic seizure. Investigators have also demonstrated that an epileptic discharge may originate in an area of cortex which has been pathologically altered by a previous ischaemia. In the investigation described here these two aspects of the problem of epilepsy have been studied. The first part of the thesis deals with vasospasms and focal cerebral ischaemia produced by mechanical and electrical stimulation of pial and cerebral arterial vessels. In the second part of the thesis is described the histological changes in the cortex and meninges resulting from the above type of stimulation and also the changes following exposure of the brain under different conditions. [...

Head injuries and their management

+127hlm.;19c

Time-Resolved Digital Image Correlation in the Scanning Electron Microscope for Analysis of Time-Dependent Mechanisms

International audienceAdvancements in the Digitial Image Correlation (DIC) technique over the past decade have greatly improved spatial resolution. However, many processes, such as plastic deformation, have a temporal component spanning from fractions of a second to minutes that has not yet been addressed in detail, particularly for DIC conducted in-situ in the scanning electron microscope (SEM). Objective: To develop a methodology for conducting time-resolved digital image correlation in the SEM for analysis of time-dependent mechanical deformation phenomena. Methods: Microscope and electron beam scanning parameters that influence the rate at which time-resolved DIC information is mapped are experimentally investigated, providing a guide for use over a range of timescales and resolutions. Results: Time-resolved DIC imaging is demonstrated on a Ti-7Al alloy, where slip band propagation is resolved with imaging dwell times of seconds. The limits of strain resolution and strain collection speeds are analyzed. Conclusions: The new developed methodology can be applied to a wide range of materials loaded in-situ to quantify time-dependent plastic deformation phenomena