Learning Recursive Segments for Discourse Parsing

Automatically detecting discourse segments is an important preliminary step towards full discourse parsing. Previous research on discourse segmentation have relied on the assumption that elementary discourse units (EDUs) in a document always form a linear sequence (i.e., they can never be nested). Unfortunately, this assumption turns out to be too strong, for some theories of discourse like SDRT allows for nested discourse units. In this paper, we present a simple approach to discourse segmentation that is able to produce nested EDUs. Our approach builds on standard multi-class classification techniques combined with a simple repairing heuristic that enforces global coherence. Our system was developed and evaluated on the first round of annotations provided by the French Annodis project (an ongoing effort to create a discourse bank for French). Cross-validated on only 47 documents (1,445 EDUs), our system achieves encouraging performance results with an F-score of 73% for finding EDUs.Comment: published at LREC 201

Reply to comment by A. Revil and N. Linde on 'Streaming potential dependence on water-content in Fontainebleau sand'

International audienceRevil and Linde recently commented our paper concerning streaming potential (SP) measurements in unsaturated sand during drainage experiments. This comment suggests that the approach used to infer SP coefficients was inappropriate for unsaturated conditions, and therefore yielded wrong conclusions and 'unphysical' results regarding the behaviour of the relative SP coefficient. This reply argues that even if in Allègre et al. we neglected some secondary electrokinetic sources, the resulting conclusions are still representative of the behaviour of the true SP coefficient, and that the remarks of Revil & Linde arose from a misunderstanding of the drainage experiment conditions. We also find support for our results from a comparison between our observations and previous experimental studies

Streaming potential dependence on water-content in Fontainebleau sand

The final version is available on www.blackwell-synergy.comInternational audienceThe electrokinetic potential results from the coupling between the water flow and the electrical current because of the presence of ions within water. The electrokinetic coupling is well described in fluid-saturated media, however its behaviour under unsaturated flow conditions is still discussed. We propose here an experimental approach to investigate streaming potential variations in sand at unsaturated conditions. We present for the first time continuous records of the electrokinetic coefficient as a function of water content. Two drainage experiments have been performed within a column filled with a clean sand. Streaming potential measurements are combined with water pressure and water content measurements every 10 centimeters along the column. In order to model hydrodymanics during the experiments, we solve Richards equation coupled with an inverse problem to estimate the hydraulic parameters of the constitutive relations between hydraulic conductivity, water pressure and water content. The electrokinetic coefficient $C$ shows a more complex behaviour for unsaturated conditions than it was previously reported and cannot be fitted by the existing models. The electrokinetic coefficient increases first when water saturation decreases from 100\% to about 65\% - 80\%, and then decreases as the water saturation decreases, whereas all previous works described a monotone decrease of the normalized electrokinetic coupling as water saturation decreases. We delimited two water saturation domains, and deduced two different empirical laws describing the evolution of the electrokinetic coupling for unsaturated conditions. Moreover we introduce the concept of the electrokinetic residual saturation $S_w^{r,ek}$, which allows us to propose a new model derived from the approach of the relative permeability used in hydrodynamics