Internal charge behaviour of nanocomposites

The incorporation of 23 nm titanium dioxide nanoparticles into an epoxy matrix to form a nanocomposite structure is described. It is shown that the use of nanometric particles results in a substantial change in the behaviour of the composite, which can be traced to the mitigation of internal charge when a comparison is made with conventional TiO2 fillers. A variety of diagnostic techniques (including dielectric spectroscopy, electroluminescence, thermally stimulated current, photoluminescence) have been used to augment pulsed electro-acoustic space charge measurement to provide a basis for understanding the underlying physics of the phenomenon. It would appear that, when the size of the inclusions becomes small enough, they act co-operatively with the host structure and cease to exhibit interfacial properties leading to Maxwell-Wagner polarization. It is postulated that the particles are surrounded by high charge concentrations in the Gouy-Chapman-Stern layer. Since nanoparticles have very high specific areas, these regions allow limited charge percolation through nano-filled dielectrics. The practical consequences of this have also been explored in terms of the electric strength exhibited. It would appear that there was a window in which real advantages accrue from the nano-formulated material. An optimum loading of about 10% (by weight) is indicated

Origin of thickness dependent dc electrical breakdown in dielectrics

A model based on space charge dynamics under high dc electric field has been proposed to explain commonly observed thickness dependent breakdown of polymeric material. The formation and dynamics of space charge will result in local electric field enhancement that has a direct impact on dielectric breakdown. The simulation results show that the breakdown depends on the sample thickness with a power index of 0.143, indicating the space charge and its dynamics are responsible for thickness dependent breakdown. The model also predicts the effect of voltage ramping rate on the electrical breakdown strength

Rwanda reconsidered

On April 6, 1994, the airplane returning the President of Rwanda home was shot down. After appearing to have achieved a negotiated end to the countries ongoing civil war, the nation was now plunged into an ethnically motivated genocide with horrendous results. What led the extremist elements of the Presidents ruling elite class to view this alternative as a plausible solution to the loss of power and prestige they would incur with implementation of the peace accords? To answer this question, this thesis examines how Rwanda's two ethnic groups were manipulated to ethnically stratify the country. After independence and a reversal of ethnic control, the new regionally based elites consistently returned to an ethnically divisive strategy to unite the population and maintain their narrow base of power over other regional elites. The onset of civil war in 1990 by exiled Tutsi refugees, coupled with international pressure for democratic reforms ultimately led to the Arusha Accords. The Accords in due course failed both because of extremist fears of the loss of their power and prestige, and the failure of the international community to back the vital provisions of the accords.http://archive.org/details/rwandreconsidere109451093

Kreuz und quer durch Marokko : Kultur- und Sittenbilder aus dem Sultanat des Westens ; Mit 1 Taf., 163 Abb. im Text und 1 Übersichtskt.

Von Otto C. ArtbauerIn Fraktu