École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Nonlinear system. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Light-assisted cold chemical reactions of barium ions with rubidium atoms

Abstract: Light-assisted reactive collisions between laser-cooled Ba+ ions and Rb atoms were studied in an ion–atom hybrid trap. The reaction rate was found to strongly depend on the electronic state of the reaction partners with the largest rate constant [7(2) × 10−11 cm3 s−1] obtained for the excited Ba+(6s)+Rb(5p) reaction channel. Similar to the previously studied Ca++Rb system, charge transfer and radiative association were found to be the dominant reactive processes. The generation of molecular ions by radiative association could directly be observed by their sympathetic cooling into a Coulomb crystal. Potential energy curves up to the Ba+(6s)+Rb(5p) asymptote and reactive-scattering cross sections for the radiative processes were calculated. The theoretical rate constant obtained for the lowest reaction channel Ba+(6s)+Rb(5s) is compatible with the experimental estimates obtained thus far.

Statistical Analysis of the MUSIC Algorithm in the Presence of Modeling Errors, Taking Into Account the Resolution Probability

Abstract: This paper considers the statistical performance of the MUSIC method under the condition that two closely spaced sources impinging on an array of sensors are effectively resolved, i.e., the spectrum exhibits two peaks in the neighborhood of the true directions-of-arrival (DOA). The MUSIC algorithm is known to have an infinite resolution power in theory. However, in the presence of modeling errors, sources can not be resolved with certainty, even if the array correlation matrix is perfectly known. The focus of this paper is to predict the bias and variance of the DOA estimates taking into account the possible resolution failure of MUSIC. This performance prediction, based on our recent mathematical investigation, is new to the best of our knowledge. A general mathematical framework to derive closed form expressions of the bias and variance versus the model mismatch, conditioned on a general statistical resolution test is proposed. In order to illustrate our mathematical approach, statistical tests with one and two conditions, respectively, are investigated. The accuracy of the performance prediction is illustrated in a simulation study. It is found that the proposed approach outperforms the “classical” technique, which ignores the possible resolution failure of the MUSIC algorithm. Therefore, our results provide better tools for determining the necessary antenna calibration accuracy to achieve some targeted specifications on the estimator performance.

Π-Stacking Functionalization of Carbon Nanotubes through Micelle Swelling†

Abstract: We report on a new, original and efficient method for pi-stacking functionalization of single-wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single-wall carbon nanotubes and porphyrin molecules. We developed a micelle-swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non-water-soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.

On the use of reservation-based autonomous vehicles for demand management

Abstract: Automated mobility on demand is foreseen as the future of urban passenger mobility. While mixed-traffic for autonomous and conventional vehicles could be considered, separation amplifies the benefits of automation. Combined with mobility as a service, separation also opens new possibilities in terms of demand management. We consider in this paper a single bottleneck dynamic framework, in which the capacity of a freeway is dedicated either to conventional or to autonomous vehicles. Users of conventional vehicles freely choose their departure time from home and compete for the best departure times from the bottleneck. Users of autonomous vehicles need to book their trip in advance. As the number of time slots available for booking does not exceed the capacity, booking users are guaranteed no delay at the bottleneck. An individual-specific cooperation cost is introduced in the modeling framework. We then investigate how a central planner should allocate the capacity to these two vehicle types depending on the regime (laissez-faire, welfare- or profit-maximizing). Two major findings are that the equilibrium demand split Pareto-dominates the case with only conventional cars and that the social cost difference between equilibrium and socially optimal demand splits is small compared to their benefits. Although the Pareto-improvement result may not hold for every single user in the case of richer heterogeneity, it remains a key advantage of our booking scheme. Profit-maximizing strategies however turn out to be hardly compatible with welfare maximization.