Anomalous fluctuation regimes at the FFLO transition

Recently some experimental evidences have been obtained in favour of the existence of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state in heavy-fermion superconductor CeCoIn_{5} and organic superconductor -(BETS)_{2}FeCl_{4}. However the unambiguous identification of FFLO state remains very difficult. We present the theoretical studies of the Gaussian fluctuations near the tricritical point (where the FFLO modulation appears) and demonstrate that the behavior of the fluctuational specific heat, paraconductivity and diamagnetism is qualitatively different from the usual superconducting transition. Special values of the critical exponent and the crossovers between different fluctuational regimes may provide a unique test for the FFLO state appearance.Comment: 6 pages, 2 figures. Work supported by ANR Extreme Conditions Correlated Electrons (ANR-06-BLAN-0220

Weighted Sum Rate Maximization for Downlink OFDMA with Subcarrier-pair based Opportunistic DF Relaying

This paper addresses a weighted sum rate (WSR) maximization problem for downlink OFDMA aided by a decode-and-forward (DF) relay under a total power constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is proposed. Specifically, user message bits are transmitted in two time slots. A subcarrier in the first slot can be paired with a subcarrier in the second slot for the DF relay-aided transmission to a user. In particular, the source and the relay can transmit simultaneously to implement beamforming at the subcarrier in the second slot. Each unpaired subcarrier in either the first or second slot is used for the source's direct transmission to a user. A benchmark protocol, same as the proposed one except that the transmit beamforming is not used for the relay-aided transmission, is also considered. For each protocol, a polynomial-complexity algorithm is developed to find at least an approximately optimum resource allocation (RA), by using continuous relaxation, the dual method, and Hungarian algorithm. Instrumental to the algorithm design is an elegant definition of optimization variables, motivated by the idea of regarding the unpaired subcarriers as virtual subcarrier pairs in the direct transmission mode. The effectiveness of the RA algorithm and the impact of relay position and total power on the protocols' performance are illustrated by numerical experiments. The proposed protocol always leads to a maximum WSR equal to or greater than that for the benchmark one, and the performance gain of using the proposed one is significant especially when the relay is in close proximity to the source and the total power is low. Theoretical analysis is presented to interpret these observations.Comment: 8 figures, accepted and to be published in IEEE Transactions on Signal Processing. arXiv admin note: text overlap with arXiv:1301.293

Mathematics education (research) liberated from teaching and learning: Towards (the future of) doing mathematics

Now, what do you make of that? We want to discuss mathematics education, and research in mathematics education (we don’t really need to specify, hence the parenthesis). And we want to address teaching and learning (mathematics, but we skipped the parenthesis this time around because we used the word just before) in terms of not-being. You will notice, however, the provocative presence of “liberated”, a strong verb which alludes to the idea of freedom while acknowledging certain constraints: captivity, dependence, and even liability. Its selection was a bold choice. But having made such a suggestive statement (without actually saying things upfront), we hastily print a colon to bring in a potential alternative – more positive, one should hope. This alternative mentions to be about going “towards” something. If we care enough to read the next parenthesis (yep, another set!), we realize that this something does not exist yet, since it lies in the future. This something we finally name with the title’s last breath: “doing|mathematics”. For those who haven’t read our recent articles (e.g., in French, Maheux & Proulx, 2014, or in English, Maheux & Proulx, 2015), what that is will remain obscure for some time. In a certain way, it is also still mysterious for us: it is the object of our research, so we haven’t “found” it yet. We haven’t really found out what “doing|mathematics” is, or what it does. As a piece of research, this article thus also aims to help us figure some of these things out. As a result, this communication piece is not merely for you. And after all, as Von Foerster used to say, in the end you’ll know more about us than about the topic of the paper

ASTERIA In-Orbit Testing on OPSSAT: An On-Board Autonomous Orbit Control Solution Including Collision Risks Avoidance

For several years, CNES has been working on Flight Dynamics algorithms to ensure high level of autonomy for next generation of space missions. One example of these autonomous techniques is the Autonomous Orbital Control, which consists of delegating to onboard satellite system the identification, planning and realization of orbital corrections to stay in the mission reference orbit. ASTERIA, an application of on-board autonomy combining station keeping and collision risk management for the low earth orbit satellites, enables both in-track and cross-track control for different LEO missions. The on-board collision risk management process is fully integrated into the autonomous station keeping in order to maintain the satellite orbit as best as possible and to minimize mission unavailability resulting from the avoidance maneuvers. The paper aims to show the completeness of the ASTERIA concept. First, the principles of on-board orbit control with collision risk management are described with the operational concepts of such a solution. Then, the ability to operate ASTERIA is demonstrated through an in-orbit experiment performed last year on the ESA OPSSAT 3-Units CubeSat

AILiveSim : An Extensible Virtual Environment for Training Autonomous Vehicles

Virtualization technologies have become common- place both in software development as well as engineering in a more general sense. Using virtualization offers other benefits than simulation and testing as a virtual environment can often be more liberally configured than the corresponding physical envi- ronment. This, in turn, introduces new possibilities for education and training, including both for humans and artificial intelligence (AI). To this end, we are developing a simulation platform AILiveSim. The platform is built on top of the Unreal Engine game development system, and it is dedicated to training and testing autonomous systems, their sensors and their algorithms in a simulated environment. In this paper, we describe the elements that we have built on top of the engine to realize a Virtual Environment (VE) useful for the design, implementation, application and analysis of autonomous systems. We present the architecture that we have put in place to transform our simulation platform from automotive specific to be domain agnostic and support two new domains of applications: autonomous ships and autonomous mining machines. We describe the important specificity of each domain in regard to simulation. In addition, we also report the challenges encountered when simulating those applications, and the decisions taken to overcome these challenges.Peer reviewe

FLORES: Helping People to Realize Sustainable Futures

People usually know how they want their situation to change to secure a better future, but they do not always know how to change their situation. Initiatives intended to secure a better future do not always work as intended, and may have unintended side effects. Computer models can help advocates explore consequences of proposed initiatives, so they can make informed selections of alternatives, secure in the knowledge that consequences have been thoroughly investigated. By encouraging people to explore scenarios, models empower people to be more innovative and less dependent on technocrats. New software solves technical limitations, but the real issue is not software, but rather the provision of a supportive framework within which people can express and experiment with ideas. FLORES, the Forest Land Oriented Resource Envisioning System, provides such a framework to stimulate interdisciplinary collaboration between researchers, practitioners and clients. A recent prototype demonstrated the feasibility of FLORES. However, FLORES is not about software; it is about providing the means to explore the consequences of alternative scenarios. Ultimately, FLORES is not a physical package, but a user group and the interactions they have amongst themselves, and with the people involved in policy-making. Fostering this emerging network through workshops and technical support will enhance FLORES by offering a better understanding of the concept, and by allowing more people, especially those from developing countries, to influence the development of FLORES and the issues that can be explored within it