ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Residual stress & Finite element method. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

Revisiting Opinion Dynamics with Varying Susceptibility to Persuasion via Non-Convex Local Search

Abstract: We revisit the opinion susceptibility problem that was proposed by Abebe et al. [1], in which agents influence one another's opinions through an iterative process. Each agent has some fixed innate opinion. In each step, the opinion of an agent is updated to some convex combination between its innate opinion and the weighted average of its neighbors' opinions in the previous step. The resistance of an agent measures the importance it places on its innate opinion in the above convex combination. Under non-trivial conditions, this iterative process converges to some equilibrium opinion vector. For the unbudgeted variant of the problem, the goal is to select the resistance of each agent (from some given range) such that the sum of the equilibrium opinions is minimized. Contrary to the claim in the aforementioned KDD 2018 paper, the objective function is in general non-convex. Hence, formulating the problem as a convex program might have potential correctness issues. We instead analyze the structure of the objective function, and show that any local optimum is also a global optimum, which is somehow surprising as the objective function might not be convex. Furthermore, we combine the iterative process and the local search paradigm to design very efficient algorithms that can solve the unbudgeted variant of the problem optimally on large-scale graphs containing millions of nodes.

Spatial retrieval of soil reflectance from SPOT multispectral data using the empirical line method

Abstract: The use of empirical relationships to calibrate remotely sensed data has been reported by many authors, but few studies have been devoted to the specific retrieval of soil reflectance and most studies have used two calibration targets only, using few ( = 5) validation targets to assess the error in the empirical relationships. Absolute corrections based on empirical line methods have seldom been applied to satellite data, particularly Satellite pour l'Observation de la Terre (SPOT) images. In this study, which deals with bare cultivated soils, the empirical line method was used to retrieve soil reflectance from three programmed SPOT satellite images with 20 m and 10 m resolution based on independent sets of 8 calibration and 15 validation field targets of bare soil. The empirical line method was applied to orthorectified images with digital number (DN) values interpolated both with the cubic convolution and the nearest neighbour interpolation mode. Root mean squared errors (RMSEs) between corrected and measured values at calibration sites were lower than 0.56% for the two visible bands and ranged between 0.61% and 1.97% for the near-infrared band, whereas at all validation sites they were mostly lower than 2.5% except for most near-infrared bands. Such accurate results have been facilitated both by the flat topographical conditions of the Beauce region (Western Parisian Basin, France) and the homogeneous sky conditions in a small study area (2500 ha). Differences in illumination conditions in both orbital and field cases did not appear to affect the results dramatically, which suggest that even oblique viewing images can be used for such correction. Errors could also be due to changes in soil moisture and roughness related to soil management practices, or slight vegetation growth over the end of the study period. Due to spatial error, the 20-m resolution with cubic convolution mode led to a much lower performance than the 10-m images with either interpolation modes. The achieved results are generalizable to European sedimentary basins with loess deposits, where similar soils and topographic conditions are to be found over thousands of km2.

Interference, cooperation and connectivity — A degrees of freedom perspective

Abstract: We explore the interplay between interference, cooperation and connectivity in heterogeneous wireless interference networks. Specifically, we consider a 4-user locally-connected interference network with pairwise clustered decoding and show that its degrees of freedom (DoF) are bounded above by 12 over 5. Interestingly, when compared to the corresponding fully connected setting which is known to have 8 over 3 DoF, the locally connected network is only missing interference-carrying links, but still has lower DoF, i.e., eliminating these interference-carrying links reduces the DoF. The 12 over 5 DoF outer bound is obtained through a novel approach that translates insights from interference alignment over linear vector spaces into corresponding sub-modularity relationships between entropy functions.