Altitude-Loss Optimal Glides in Engine Failure Emergencies -- Accounting for Ground Obstacles and Wind

Engine failure is a recurring emergency in General Aviation and fixed-wing UAVs, often requiring the pilot or remote operator to carry out carefully planned glides to safely reach a candidate landing strip. We tackle the problem of minimizing the altitude loss of a thrustless aircraft flying towards a designated target position. Extending previous work on optimal glides without obstacles, we consider here trajectory planning of optimal gliding in the the presence of ground obstacles, while accounting for wind effects. Under simplifying model assumptions, in particular neglecting the effect of turns, we characterize the optimal solution as comprising straight glide segments between iteratively-determined extreme points on the obstacles. Consequently, the optimal trajectory is included in an iteratively-defined reduced visibility graph, and can be obtained by a standard graph search algorithm, such as A$^*$. We further quantify the effect of turns to verify a safe near-optimal glide trajectory. We apply our algorithm on a Cessna 172 model, in realistic scenarios, demonstrating both the altitude-loss optimal trajectory calculation, and determination of airstrip reachability

Strategic Posting Times over a Shared Publication Medium

International audienceWe consider a game of timing between advertisers, or other content creators, who compete for position and exposure over a shared publication medium such as an on-line classified list. Posted items (such as ads, messages, multimedia, or comments) are ordered according to their posting times, with recent posts displayed at the top positions. The effectiveness of each item depends on its current display position, as well as on a time-dependent exposure function which represents the collective exposure of the medium. It is assumed that each of a Poisson-distributed number of advertiser may choose the posting time of his item within a finite time interval, with the goal of maximizing the total exposure of this item. We formulate and the problem as a non-cooperative game between advertisers, and analyze the Nash equilibrium profile of this game in terms of existence, uniqueness, computation and efficiency. Explicit expressions are derived for the case where the relative importance of the posting positions are geometrically decreasing

Dynamic Games for analyzing competition in the Internet and in on-line social networks

International audienceThe global Internet has enabled a massive access of internauts to content. At the same time it allowed individuals to use the Internet in order to distribute content. This introduced new types of competition between content over popularity, visibility, influence, reputation and user attention. The rules of these competitions are new with respect to those of traditional media, and they are determined by the way resources are allocated through network protocols (such as page rank in search engines and recommendation systems that are widely spread in social networks). In this paper we first present in the introduction an overview of some central competition issues both in the Internet as well as in other types of networks. We then describe the model of when to send content in order to maximize the exposure of the content. In the two last sections we finally describe research on two bio-inspired tools that have bben used to study various competition aspects

Algorithms for stochastic approximations of curvature flows

©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/ICIP.2003.1246764Presented at ICIP-2003 : 2003 International Conference on Image Processing, September 14-17, 2003, Barcelona, Spain.Curvature flows have been extensively considered from a deterministic point of view. They have been shown to be useful for a number of applications including crystal growth, flame propagation, and computer vision. In some previous work G. Ben-Arous et al. (2002), we have described a random particle system, evolving on the discretized unit circle, whose profile converges toward the Gauss-Minkowsky transformation of solutions of curve shortening flows initiated by convex curves. The present note shows that this theory may be implemented as a new way of evolving curves and as a possible alternative to level set methods