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Bourdin L.,CNRS XLIM Research Institute, Limoges | Trelat E.,Paris-Sorbonne University
Automatica | Year: 2017

We consider linear–quadratic optimal sampled-data control problems, where the state evolves continuously in time according to a linear control system and the control is sampled, i.e., is piecewise constant over a subdivision of the time interval, and the cost is quadratic. As a first result, we prove that, as the sampling periods tend to zero, the optimal sampled-data controls converge pointwise to the optimal permanent control. Then, we extend the classical Riccati theory to the sampled-data control framework, by developing two different approaches: the first one uses a recently established version of the Pontryagin maximum principle for optimal sampled-data control problems, and the second one uses an adequate version of the dynamic programming principle. In turn, we obtain a closed-loop expression for optimal sampled-data controls of linear–quadratic problems. © 2017 Elsevier Ltd

Carsenat D.,CNRS XLIM Research Institute, Limoges | Decroze C.,CNRS XLIM Research Institute, Limoges
IEEE Antennas and Wireless Propagation Letters | Year: 2012

In this letter, the feasibility of a new concept of passive antenna beamformer is investigated. The main idea is to develop a (1× N)-ports device in which the weightings on output ports are applied by time-reversal operation. The control of antennas weightings is then contained in the input waveform without the need of active components or external control signals. This approach is validated experimentally by radiation pattern measurement of a four-Vivaldi-antennas array, associated to a small reverberation cell beamformer. Finally, this concept is applied to realize a passive ultrawideband (UWB) phased-array radar for target imaging. © 2012 IEEE.

Arnault F.,CNRS XLIM Research Institute, Limoges
Journal of Physics A: Mathematical and Theoretical | Year: 2012

We give a multidimensional generalization of the complete set of Bell-correlation inequalities given by Werner and Wolf (2001 Phys. Rev. A 64 032112) and by Zukowski and Brukner (2002 Phys. Rev. Lett. 88 210401), for the two-dimensional case. Our construction applies to the n-party, two-observable case, where each observable is d-valued. The inequalities obtained involve homogeneous polynomials. They define the facets of a polytope in a complex vector space of dimension d n. We detail the inequalities obtained in the case d = 3 and, from them, we recover known inequalities. We finally explain how the violations of our inequalities by quantum mechanics can be computed and could be observed, when using unitary observables. © 2012 IOP Publishing Ltd.

Dusart P.,CNRS XLIM Research Institute, Limoges | Traore S.,British Petroleum
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

Providing security in low-cost RFID (Radio Frequency Identification) tag systems is a challenging task because low-cost tags cannot support strong cryptography which needs costly resources. Special lightweight algorithms and protocols need to be designed to take into account the tag constraints. In this paper, we propose a function and a protocol to ensure pre-shared key authentication. © 2013 Springer-Verlag.

Dauliat R.,CNRS XLIM Research Institute, Limoges | Gaponov D.,CNRS XLIM Research Institute, Limoges | Benoit A.,CNRS XLIM Research Institute, Limoges | Salin F.,Eolite Lasers | And 3 more authors.
Optics Express | Year: 2013

Very large mode area, active optical fibers with a low high order mode content in the actively doped core region were designed by removing the inner cladding symmetry. The relevance of the numerical approach is demonstrated here by the investigation of a standard air-silica Large Pitch Fiber, used as a reference. A detailed study of all-solid structures is also performed. Finally, we propose new kinds of geometry for 50 μm core, all-solid microstructured fibers enabling a robust singlemode laser emission from 400 nm to 2200 nm. © 2013 Optical Society of America.

Fromenteze T.,CNRS XLIM Research Institute, Limoges | Carsenat D.,CNRS XLIM Research Institute, Limoges | Decroze C.,CNRS XLIM Research Institute, Limoges
IEEE Antennas and Wireless Propagation Letters | Year: 2013

The passive time-reversal beamformer is a 1× N ports device with {N} orthogonal channels. Beamforming is achieved using simultaneous time reversal focusing on the output ports with the only input waveform. Utilizing this method, an antenna array can be supplied with focused signals of controlled complex weights and achieve beam steering. A precorrection method is developed in this letter to normalize the weights of the output signals at the focusing time, avoiding a long optimization step of beamformer designing. The theory is developed in this letter, followed by experimental validation. © 2002-2011 IEEE.

Andres E.,CNRS XLIM Research Institute, Limoges
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

This paper is meant as a short survey on analytically defined digital geometric objects.We will start by giving some elements on digitizations and their relations to continuous geometry. We will then explain how, from simple assumptions about properties a digital object should have, one can build mathematically sound digital objects. We will end with open problems and challenges for the future. © Springer International Publishing Switzerland 2015.

Bensalma R.,CNRS XLIM Research Institute, Limoges | Larabi M.-C.,CNRS XLIM Research Institute, Limoges
Multidimensional Systems and Signal Processing | Year: 2013

Stereoscopic imaging is becoming very popular and its deployment by means of photography, television, cinema.is rapidly increasing. Obviously, the access to this type of images imposes the use of compression and transmission that may generate artifacts of different natures. Consequently, it is important to have appropriate tools to measure the quality of stereoscopic content. Several studies tried to extend well-known metrics, such as the PSNR or SSIM, to 3D. However, the results are not as good as for 2D images and it becomes important to have metrics dealing with 3D perception. In this work, we propose a full reference metric for quality assessment of stereoscopic images based on the binocular fusion process characterizing the 3D human perception. The main idea consists of the development of a model allowing to reproduce the binocular signal generated by simple and complex cells, and to estimate the associated binocular energy. The difference of binocular energy has shown a high correlation with the human judgement for different impairments and is used to build the Binocular Energy Quality Metric (BEQM). Extensive experiments demonstrated the performance of the BEQM with regards to literature. © 2012 Springer Science+Business Media, LLC.

Huynh V.N.,Quy Nhon University | Nguyen H.T.,Quy Nhon University | Thera M.,CNRS XLIM Research Institute, Limoges
Mathematical Programming | Year: 2013

In this paper, we establish some new characterizations of metric regularity of implicit multifunctions in complete metric spaces by using lower semicontinuous envelopes of the distance functions to set-valued mappings. Through these new characterizations it is possible to investigate implicit multifunction theorems based on coderivatives and on contingent derivatives as well as the perturbation stability of implicit multifunctions. © 2013 Springer-Verlag Berlin Heidelberg and Mathematical Optimization Society.

Benoist J.,CNRS XLIM Research Institute, Limoges
Journal of Global Optimization | Year: 2015

In this paper, we solve a conjecture proposed by Borwein and Sims (Fixed-point algorithms for inverse problems in science and engineering, Springer optimization and its applications, 2011) in a Hilbert space setting. For the simple non-convex example of the sphere and the line, the sequence of Douglas–Rachford iterates converges in norm to a point of the intersection except when the initial value belongs to the hyperplane of symmetry. © 2015, Springer Science+Business Media New York.

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