Isotropic Huygens dipoles and multipoles with colloidal particles

Huygens sources are elements that scatter light in the forward direction as used in the Huygens-Fresnel principle. They have remained fictitious until recently where experimental systems have been fabricated. In this letter, we propose isotropic meta-atoms that act as Huygens sources. Using clusters of plasmonic or dielectric colloidal particles, Huygens dipoles that resonate at visible frequencies can be achieved with scattering cross-sections as high as 5 times the geometric cross-section of the particle surpassing anything achievable with a hypothetical simple spherical particle. Examples are given that predict extremely broadband scattering in the forward direction over a 1000 nm wavelength range at optical frequencies. These systems are important to the fields of nanoantennas, metamaterials and wave physics in general as well as any application that requires local control over the radiation properties of a system as in solar cells or bio-sensing

Finding a Nash Equilibrium in Spatial Games is an NP-Complete Problem

We consider the class of (finite) spatial games. We show that the problem of determining whether there exists a Nash equilibrium in which each player has a payoff of at least k is NP-complete as a function of the number of players. When each player has two strategies and the base game is an anti-coordination game, the problem is decidable in polynomial time.spatial games; NP-completeness; graph K-colorability

Average tree solutions for graph games

In this paper we consider cooperative graph games being TU-games in which players cooperate if they are connected in the communication graph. We focus our attention to the average tree solutions introduced by Herings, van der Laan and Talman [6] and Herings, van der Laan, Talman and Yang [7]. Each average tree solution is defined with re- spect to a set, say T , of admissible rooted spanning trees. Each average tree solution is characterized by efficiency, linearity and an axiom of T - hierarchy on the class of all graph games with a fixed communication graph. We also establish that the set of admissible rooted spanning trees introduced by Herings, van der Laan, Talman and Yang [7] is the largest set of rooted spanning trees such that the corresponding aver- age tree solution is a Harsanyi solution. One the other hand, we show that this set of rooted spanning trees cannot be constructed by a dis- tributed algorithm. Finally, we propose a larger set of spanning trees which coincides with the set of all rooted spanning trees in clique-free graphs and that can be computed by a distributed algorithm.

Complete multipolar description of reflection and transmission across a metasurface for perfect absorption of light

International audienceRelating the electromagnetic scattering and absorption properties of an individual particle to the reflection and transmission coefficients of a two-dimensional material composed of these particles is a crucial concept that has driven both fundamental and applied physics. It is at the heart of boththe characterization of material properties as well as the phase and amplitude engineering of a wave. Here we propose a multipolar description of the reflection and transmission coefficients across a monolayer of particles using a vector spherical harmonic decomposition. This enables us to providea generalized condition for perfect absorption which occurs when both the so-called generalized Kerker condition is reached and when the superposition of odd and even multipoles reaches a critical value. Using these conditions, we are able to propose two very different designs of two-dimensional materials that perfectly absorb a plane electromagnetic wave under normal incidence. One is an infinite array of silica microspheres that operates at mid-infrared frequencies, while the other is an infinite array of germanium nano-clusters that operates at visible frequencies. Both systems operate in a deeply multipolar regime. Our findings are important to the metamaterials and metasurfaces communities who design materials mainly restricted to the dipolar behavior of individual resonators,as well as the self-assembly and nanochemistry communities who separate the individual particle synthesis from the materials assembly

Potential of Radiotelescopes for Atmospheric Line Observations: I. Observation Principles and Transmission Curves for Selected Sites

Existing and planned radiotelescopes working in the millimetre (mm) and sub-millimetre wavelengths range provide the possibility to be used for atmospheric line observations. To scrutinize this potential, we outline the differences and similarities in technical equipment and observing techniques between ground-based aeronomy mm-wave radiometers and radiotelescopes. Comprehensive tables summarizing the technical characteristics of existing and future (sub)-mm radiotelescopes are given. The advantages and disadvantages using radiotelescopes for atmospheric line observations are discussed. In view of the importance of exploring the sub-mm and far-infrared wavelengths range for astronomical observations and atmospheric sciences, we present model calculations of the atmospheric transmission for selected telescope sites (DOME-C/Antarctica, ALMA/Chajnantor, JCMT and CSO on Mauna Kea/Hawaii, KOSMA/Swiss Alpes) for frequencies between 0 and 2000 GHz (150 micron) and typical atmospheric conditions using the forward model MOLIERE (version~5). For the DOME-C site, the transmission over a larger range of up to 10 THz (30 micron) is calculated in order to demonstrate the quality of an earth-bound site for mid-IR observations. All results are available on a dedicated webpage (http://transmissioncurves.free.fr)Comment: Planetary and Space Science accepted (in press), see also website http://transmissioncurves.free.f

Saturation of the Raman amplification by self-phase modulation in silicon nanowaveguides

We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowaveguides, causing it to saturate. A simple calculation of the Raman gain coefficient from the measured broadened output pump spectra perfectly matches the saturated behavior of the amplified Raman signal observed experimentally at different input pump powers.Comment: Accepted for publications in Applied Physics Letter

Mechanical properties of children cortical bone: a bimodal characterization

International audienceFor cortical bone, important changes of the elastic properties values have been clearly shown in ageing but not in childhood, furthermore recent works considered osteoporosis as a pediatric disease with geriatric consequences and children are concerned by specific infantile osteopathologies. That is why there is a strong interest in the characterisation of the growing process of children bone. However, few mechanical properties of cortical growing bone are available in literature and do not yield to gold standards. In this work, we have analysed surgery waste (bone transplantation) from long bone (fibula). In a first step, a non destructive method was used to evaluate the velocity of ultrasonic waves from which the acoustic Young's modulus Ea is calculated using the difference of sound path duration and the mass density. Then, in a second step, a destructive method was used to obtain mechanical Young's modulus Em using a 3-point microbending. The children samples (4 to 16 year old) show an average Ea and na of 15.5 GPa (+/- 3.4) and 0.24 (+/- 0.08) at 10 MHz , and an average Em of 9.1 GPa (+/- 3.5). Ea and na are in the same range for children and seniors but a linear correlation between Ea and Em is found only for the fourteen samples of the children group

Children cortical bone characterisation: the ultrasonic issue

International audienceNowadays there is a strong interest in the characterization of the growing process of children bone. Recent works considered osteoporosis as a pediatric disease with geriatric consequences and children are concerned by specific infantile osteo-pathologies. However, few mechanical properties of cortical growing bone are available in literature and do not yield to gold standards. The goal of this study is to evaluate the validity of ultrasonic characterization of elastic properties for growing bone. Nine surgery wastes from fibula auto-transplants (5 to 16 years old children with accordance of French ethical committee) are included in a two-step method process. A non-destructive ultrasonic evaluation (7 and 10 MHz) yields to acoustic Youngs modulus (Ea) and a micro-three point bending test yields to Youngs modulus (E). Ultrasonic testing provides an average Ea of 15.2 GPa (+/- 2.9) at 7 MHz and 15.49 GPa (+/- 3.95) at 10 MHz, and micro-flexion an average E of 10.13 GPa (+/- 5.29). A linear correlation between Ea and E is found (R2 value is 0.78 at 7 MHz and 0.79 at 10 MHz). To our knowledge, this is the highest R2 between destructive and non-destructive method found in literature for human cortical bone

Ten reasons for performing hemodynamic monitoring using transesophageal echocardiography.

International audienc

Expérience : le module Ecriture théâtrale

Le module Ecriture théâtrale de la Faculté des Lettres de Besançon est un module optionnel de deuxième année. Il est ouvert aux étudiants de Lettres, de langues et d'autres disciplines. Ce module s'insère dans un ensemble de modules théâtraux qui sont délivrés par la Faculté. Son but est de faire découvrir aux étudiants, de façon très concrète, la genèse d'un spectacle. Les étudiants doivent rédiger une pièce ou un fragment de pièce, qu'ils jouent ensuite. Auteurs et acteurs, ils essaient don..