A cubic defining algebra for the Links-Gould polynomial

We define a finite-dimensional cubic quotient of the group algebra of the braid group, endowed with a (essentially unique) Markov trace which affords the Links-Grould invariant of knots and links. We investigate several of its properties, and state several conjectures about its structure

Fibre gratings for hydrogen sensing

Liquid hydrogen has been intensively used in aerospace applications for the past 40 years and is of great interest for future automotive applications. Following major explosive risks due to the use of hydrogen in air, several studies were carried out in order to develop optical fibre sensors for the detection of hydrogen leakage. This paper aims at the presentation of new hydrogen sensors based on the use of fibre Bragg gratings (FBG) and long period gratings (LPG) coated by palladium nanolayers. The sensing principle based on the palladium–hydrogen interaction is presented, as well as experimental results. It is shown that both techniques could be used for hydrogen sensing but with a sensitivity enhanced by a factor up to 500 when using a LPG sensor. FBG sensors appear to be pure strain sensors and LPG sensors are mainly based on the coupling between the cladding modes and evanescent or surface plasmon waves. Preliminary results obtained with an in-fibre Mach–Zehnder interferometer configuration with in-series LPG sensors are also presented. They show potential interest to compensate for the thermal sensitivity of the fibre gratings

Discriminated measures of strain and temperature in metallic specimen with embedded superimposed long and short fibre Bragg Gratings

International audienceWe propose a superimposed fibre Bragg gratings device to measure, localize and discriminate strain and temperature effects simultaneously for structural health monitoring purpose. Long period grating (LPG) and fibre Bragg grating (FBG) exhibit different responses to an applied solicitation, thus, strain and temperature influences can be determined separately by measuring the corresponding wavelength shifts. In this paper we present a configuration based on the use of these two gratings types: a LPG and a FBG written in the same fibre section which allows us to discriminate the contributions of these two main solicitations. The sensor is calibrated in a temperature range from 22°C to 120°C, and in a strain range from 0 to 1400 µε. The reported errors are estimated to be within ± 0.4°C and ±5µε respectively. Our sensor is compared to the ones suggested in literature for the discrimination between strain and temperature with Bragg gratings. We propose a parameter E which allows to compare the relative uncoupling efficiency of those techniques. These sensors were embedded and tested in metallic material plates for a validation purpose of structural health monitoring

Highly Sensitive Miniaturized Refractive Index Sensor Based on Au-Ag Surface Gratings on a Planar Optical Waveguide

International audienceWe present the theoretical study of a novel highly sensitive, miniaturized, integrated optic refractive index sensor based on a Au-Ag surface grating. The grating is considered to be made of alternate layers of equi-thick Au and Ag regions along the direction of propagation, on the surface of the waveguide. Due to the same thickness of both the metals, the surface plasmon polaritons (SPP) for both metals have their field maxima at the same transverse distance, leading to an increased modal overlap in the grating region and hence a reduced grating length. An exact coupled-mode-theory based on the local mode matching has been used to analyze the mode coupling between the guided mode and the SPP. It has been shown that the proposed design requires nearly one fourth of the grating length as compared to the corrugated metal grating for the same metal thickness. Further, for co-propagating mode coupling (LPG based sensor) the structure is found to be maximum sensitive at an optimum metal thickness, however, such an optimum metal thickness does not exist for counter-propagating coupling (FBG based sensor)

A fast rotation period and large amplitude for PHA 2021 NY1

We report optical light curve observations of the near earth asteroid 2021 NY1. It was first observed with Pan-STARRS 1, Haleakala, on 2021, July 7 and has been classified by the Minor Planet Center as a potentially hazardous asteroid

Influence of grain growth on CO2 ice spectroscopic profiles : Modelling for dense cores and disks

Interstellar dust grain growth in dense clouds and protoplanetary disks, even moderate, affects the observed interstellar ice profiles as soon as a significant fraction of dust grains is in the size range close to the wave vector at the considered wavelength. The continuum baseline correction made prior to analysing ice profiles influences the subsequent analysis and hence the estimated ice composition, typically obtained by band fitting using thin film ice mixture spectra. We model the effect of grain growth on ice mantle spectroscopic profiles, focusing on CO2 to see how it can affect interstellar ice mantle spectral analysis and interpretation. Using the Discrete Dipole Approximation for Scattering and Absorption of Light, the mass absorption coefficients of distributions of grains composed of ellipsoidal silicate cores with water and carbon dioxide ice mantles are calculated. A few other ice mantle compositions are also calculated. We explore the size distribution evolution from dense clouds to simulate the first steps of grain growth up to three microns in size. The results are injected into RADMC-3D full scattering radiative transfer models of spherical clouds and protoplanetary disk templates to retrieve observable spectral energy distributions. We focus on calculated profile of the CO2 antisymmetric stretching mode ice band profile at 4.27 microns, a meaningful indicator of grain growth. The observed profiles toward dense cores with the Infrared space observatory and Akari satellites already showed profiles possibly indicative of moderate grain growth.The observation of protoplanetary disks at high inclination with the JWST should present distorted profiles that will put constraints on the extent of dust growth. The more evolved the dust size distribution, the more the extraction of the ice mantle composition will require both understanding and taking into account grain growth.Comment: 19 pages, 16 figure

Efficient and Controllable Silver Nanoparticles Generation in Ion-exchanged Soda-lime Glasses by Simultaneous Heat Treatment and UV Exposure

International audienceIn this paper, we report on the space-selective precipitation of silver nanoparticles in ion-exchanged silica-based glasses, by simultaneous continuous wave UV exposure and heat treatment. Changes in the absorption spectrum of the glass are explained by the growth of the silver nanoparticles when increasing the UV power density and the annealing temperature. Nanoparticles of average diameter 40 nm have been observed, whereas silver nanoparticles formed under laser exposure at room temperature are usually limited to few nanometers in diameters

Real time in-situ pulsed magnetic field coil deformation measurements with fiber Bragg sensors

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Croissance de nanoparticules d'argent par insolation laser ultra-violette continue dans des verres soda-lime

International audienceDes nanoparticules (NP) d'argent sont obtenues en grande concentration dans des verres soda-lime par insolation laser continue à 244 nm. L'originalité de cette communication réside dans la précipitation locale de grosses NP dont le diamètre peut atteindre 250 nm, en forte concentration, contrairement aux NP formées par irradiation laser pulsée, dont le diamètre n'excède pas quelques nm. Nous montrons que le diamètre des NP dépend directement de la densité de puissance utilisée et que les plus grosses NP sont formées par coalescence des plus petites. Les zones insolées avec la plus forte densité de puissance présente un caractère quasi-métallique très réfléchissant