School for Advanced Studies in the Social Sciences

About: School for Advanced Studies in the Social Sciences is a facility organization based out in Villejuif, France. It is known for research contribution in the topics: Population & Politics. The organization has 1230 authors who have published 2084 publications receiving 57740 citations. The organization is also known as: Ecole des Hautes Etudes en Sciences Sociales & EHESS.

Optimal geometry of transportation networks.

Abstract: Motivated by the shape of transportation networks such as subways, we consider a distribution of points in the plane and ask for the network $G$ of given length $L$ that is optimal in a certain sense. In the general model, the optimality criterion is to minimize the average (over pairs of points chosen independently from the distribution) time to travel between the points, where a travel path consists of any line segments in the plane traversed at slow speed and any route within the subway network traversed at a faster speed. Of major interest is how the shape of the optimal network changes as $L$ increases. We first study the simplest variant of this problem where the optimization criterion is to minimize the average distance from a point to the network, and we provide some general arguments about the optimal networks. As a second variant we consider the optimal network that minimizes the average travel time to a central destination, and discuss both analytically and numerically some simple shapes such as the star network, the ring or combinations of both these elements. Finally, we discuss numerically the general model where the network minimizes the average time between all pairs of points. For this case, we propose a scaling form for the average time that we verify numerically. We also show that in the medium-length regime, as $L$ increases, resources go preferentially to radial branches and that there is a sharp transition at a value $L_c$ where a loop appears.

A Geometric Model of Multi-scale Orientation Preference Maps via Gabor Functions

Abstract: In this paper we present a new model for the generation of orientation preference maps in the primary visual cortex (V1), considering both orientation and scale features. First we undertake to model the functional architecture of V1 by interpreting it as a principal fiber bundle over the 2-dimensional retinal plane by introducing intrinsic variables orientation and scale. The intrinsic variables constitute a fiber on each point of the retinal plane and the set of receptive profiles of simple cells is located on the fiber. Each receptive profile on the fiber is mathematically interpreted as a rotated Gabor function derived from an uncertainty principle. The visual stimulus is lifted in a 4-dimensional space, characterized by coordinate variables, position, orientation and scale, through a linear filtering of the stimulus with Gabor functions. Orientation preference maps are then obtained by mapping the orientation value found from the lifting of a noise stimulus onto the 2-dimensional retinal plane. This corresponds to a Bargmann transform in the reducible representation of the $$\text {SE}(2)=\mathbb {R}^2\times S^1$$ group. A comparison will be provided with a previous model based on the Bargmann transform in the irreducible representation of the $$\text {SE}(2)$$ group, outlining that the new model is more physiologically motivated. Then, we present simulation results related to the construction of the orientation preference map by using Gabor filters with different scales and compare those results to the relevant neurophysiological findings in the literature.

Weak Ties and Expertise: Crossing Technological Boundaries

Abstract: In this article, we question how new technological traits can penetrate cohesive social groups and spread. Based on ethnographic narratives and following studies in sociology, the hypothesis is that not only weak ties are important for linking otherwise unconnected groups and introducing new techniques but also that expertise is required. In order to test this hypothesis, we carried out a set of field experiments in northern India where the kiln has been adopted recently. Our goal was to measure the degree of expertise of the potters distributed between early and late adopters of the kiln. Our results are discussed in the light of oral interviews. Our conclusions suggest that expertise is a necessary, albeit not sufficient, condition for weak ties to act as bridges and thereby for new techniques to spread. As an example, they explain how turntables could have been adopted by potters from the northern Levant during the third millennium BC.