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International audience; Recent experimental studies demonstrated that Electrostatic Force Distance Curve (EFDC) can be used for space charge probing in thin dielectric layers. The main advantage of this method is its high sensitivity to charge localization. In this paper, we developed an inverse method to recover the space charge using only the EFDC.

Techniques derived from the near-field microscopies and particularly the Atomic Force Microscopy (AFM) are presented as alternative techniques for measurement of space charge compared to classical techniques due to their high sensitivity to the electrostatic force and a better resolution (≈ nm). One of the AFM derivative techniques which allow obtaining information on the charge state of the dielectric materials is based on the technique of Force Distance Curves (FDC) obtained by cycle of approach and retracts between the AFM probe and the dielectric. In this paper, three-Dimensional (3D) simulation results for the electrostatic force between an Atomic Force Microscope (AFM) tip and the surface of a dielectric are presented for different AFM tip geometries. The first aim is to analyse the effect of the geometric parameter on force-distance curves without contribution of the cantilever as AFM detection mode for electrostatic charges. At the second time the sensor is composed of a cantilever supporting a conical tip terminated by a spherical apex, we investigate in a second step is to see the effect of the cantilever on force distance curve. Simulation results are shown and compared with experimental data in order to validate our approach., Fundação para a Ciência e a Tecnologia (FCT)

Electrical insulation ages and degrades until its eventual failure under electrical stress. One cause of this relates to the movement and accumulation of charge within the insulation. The emission of a low level of light from polymeric materials while under electrical stressing occurs before the onset of currently detectable material degradation. This light is known as electroluminescence (EL) and under an ac electric field is thought to relate to the interaction of charge in close proximity to the electrode-polymer interface. Understanding the cause of this light emission gives a very high-resolution method of monitoring charge interaction and its influence on material ageing. A possible cause of this light emission is the bipolar charge recombination theory. This theory involves the injection, trapping and recombination of charge carriers during each half cycle of the applied field [1]. This work compares two models that to simulate the EL emission according to this bipolar charge recombination theory. Model 1 assumes a fixed space charge region and all injected charge is uniformly distributed in this region with charges able to either become trapped or to recombine with opposite polarity charge carriers [2]. This recombination relates directly the excitation needed for the emission of a photon of light as measured in experiments. Model 2 develops on this by accounting for the transport and extraction of charge with an exponential distribution of trap levels rather than a uniform distribution [3]. Figure 1 shows a good correlation between the two models and experimental data. The full paper will describe the models in more detail and present results comparing the simulated and experimental results under various applied waveforms. Model 1 and model 2 both provide a good correlation with experimental data but model 2 allows a greater understanding of the space charge profile in the region close to the electrodes as well as the shape of the conduction current. Further work involves developing these models to support changes in the charge trapping profiles due to material ageing and supporting simulated results with measured conduction current.

We describe three elementary models in three dimensional subelliptic geometry which correspond to the three models of the Riemannian geometry (spheres, Euclidean spaces and Hyperbolic spaces) which are respectively the SU(2), Heisenberg and SL(2) groups. On those models, we prove parabolic Li-Yau inequalities on positive solutions of the heat equation. We use for that the $\Gamma_{2}$ techniques that we adapt to those elementary model spaces. The important feature developed here is that although the usual notion of Ricci curvature is meaningless (or more precisely leads to bounds of the form $-\infty$ for the Ricci curvature), we describe a parameter $\rho$ which plays the same role as the lower bound on the Ricci curvature, and from which one deduces the same kind of results as one does in Riemannian geometry, like heat kernel upper bounds, Sobolev inequalities and diameter estimates.

The goal of this paper is to define and study a notion of fractional Brownian motion on a Lie group. We define it as at the solution of a stochastic differential equation driven by a linear fractional Brownian motion. We show that this process has stationary increments and satisfies a local self-similar property. Furthermore the Lie groups for which this self-similar property is global are characterized. Finally, we prove an integration by parts formula on the path group space and deduce the existence of a density.

It is shown that the law of an SDE driven by fractional Brownian motion with Hurst parameter greater than 1/2 has a smooth density with respect to Lebesgue measure, provided that the driving vector fields satisfy H\"ormander's condition. The main new ingredient of the proof is an extension of Norris' lemma to this situation.

It is shown that the law of an SDE driven by fractional Brownian motion with Hurst parameter greater than 1/2 has a smooth density with respect to Lebesgue measure, provided that the driving vector fields satisfy H��rmander's condition. The main new ingredient of the proof is an extension of Norris' lemma to this situation.

The Marmul field lies in the Dhofar province of the Sultanate of Oman. The heavy oil accumulation was discovered in 1956 by Dhofar Cities Services who drilled five wells, but it was not considered commercial and operations were abandoned. Petroleum Development Oman acquired the concession in 1969. Producible oil occurs in Paleozoic clastic rocks overlain unconformably by a Cretaceous sealing shale. Initial appraisal showed the complex nature of the reservoir distribution to be due to its glacial to periglacial environment of deposition and a simple geologic model was conceived. Seismic impedance contrast at the seal's unconformity surface was then used as a predictive tool to differentiate glacial waste zones (tillites) from periglacial reservoirs and as a support for the continuing appraisal and development drilling. The glacial to periglacial geologic model was progressively refined by further development drilling. The appraisal effort based on geologic and seismic impedance models was then pursued toward possible additional younger stacked reservoirs stratigraphically trapped at the periphery of the field. Drilling proved these reservoirs to be separate from the main field and oil bearing. The unraveling of the field's complex trapping mechanisms and the refinement of the geologic models needed for primary development and secondary recovery schemes could only be achieved through an integrated approach by geologists and geophysicists.