Determining the Complex Refractive Index of Materials in the Far-Infrared from Terahertz Time-Domain Data

Terahertz time‐domain spectroscopy is a well‐established technique to study the far‐infrared electromagnetic response of materials. Measurements are broadband, fast, and performed at room temperature. Moreover, compact systems are nowadays commercially available, which can be operated by nonspecialist staff. Thanks to the determination of the amplitude and phase of the recorded signals, both refractive index and absorption coefficient of the sample material can be obtained. However, determining these electromagnetic parameters should be performed cautiously when samples are more or less transparent. In this chapter, we explain how to extract the material parameters from terahertz time‐domain data. We list the main sources of error, and their contribution to uncertainties. We give rules to select the most adapted technique for an optimized characterization, depending on the transparency of the samples, and address the case of samples with strong absorption peaks or exhibiting scattering

La culture extrême, une approche à la co-construction de la culture organisationnelle

Ce mémoire propose de conceptualiser la culture organisationnelle d’un angle nouveau. Mary Jo Hatch (1993), dans son modèle de Cultural Dynamics, soutient que la culture d’une entreprise favorise la modulation de l’identité des individus y travaillant. Partant de cette affirmation, je me questionne à savoir si l’inverse est aussi possible. La culture de l’organisation et l’identité des individus y travaillant peuvent-ils évoluer dans une dynamique de co-construction? Afin d’étudier ce phénomène, j’ai mené une série d’entrevues selon la méthode du récit de vie au sein d’Empire Sports, une chaîne québécoise de boutiques de vente au détail d’articles de sports extrêmes. En me basant sur la théorie des communautés de pratiques, j’ai analysé et interprété les résultats obtenus lors des entrevues. J’arrive à identifier et à préciser ce phénomène de co-construction que j’interprète à l’aide d’un nouveau concept appelé la culture extrême. Comme cette recherche est exploratoire, les conclusions ouvrent la possibilité d’approfondir davantage les connaissances à propos de la culture extrême en l’examinant dans d’autres contextes organisationnels.This Master’s thesis proposes looking at organizational culture in a new light. In her model of cultural dynamics, Mary Jo Hatch (1993) suggests that a company’s culture influences the identity of the individuals working there. Starting from this affirmation, I ask if the inverse is also possible. Do organizational culture and individual identities evolve together in a dynamic of co-construction? Using a method inspired by the « life story », I conducted a series of interviews at Empire Sports, a Quebec chain of boutiques specializing in extreme sports. I use the communities of practice framework to analyze and interpret the intreviews. My results identify a phenomenon of co-construction at work. I interpret this using a new concept which I call « extreme culture ». The conclusions of this exploratory research suggest that further research in other organizational contexts could be useful in deepening of the concept of extreme culture

Faster and Cheaper Energy Demand Forecasting at Scale

Energy demand forecasting is one of the most challenging tasks for grids operators. Many approaches have been suggested over the years to tackle it. Yet, those still remain too expensive to train in terms of both time and computational resources, hindering their adoption as customers behaviors are continuously evolving. We introduce Transplit, a new lightweight transformer-based model, which significantly decreases this cost by exploiting the seasonality property and learning typical days of power demand. We show that Transplit can be run efficiently on CPU and is several hundred times faster than state-of-the-art predictive models, while performing as well

White Matter Information Flow Mapping from Diffusion MRI and EEG

International audienceThe human brain can be described as a network of specialized and spatially distributed regions. The activity of individual regions can be estimated using electroencephalography and the structure of the network can be measured using diffusion magnetic resonance imaging. However, the communication between the different cortical regions occurring through the white matter, coined information flow, cannot be observed by either modalities independently. Here, we present a new method to infer information flow in the white matter of the brain from joint diffusion MRI and EEG measurements. This is made possible by the millisecond resolution of EEG which makes the transfer of information from one region to another observable. A subject specific Bayesian network is built which captures the possible interactions between brain regions at different times. This network encodes the connections between brain regions detected using diffusion MRI tractography derived white matter bundles and their associated delays. By injecting the EEG measurements as evidence into this model, we are able to estimate the directed dynamical functional connectivity whose delays are supported by the diffusion MRI derived structural connectivity. We present our results in the form of information flow diagrams that trace transient communication between cortical regions over a functional data window. The performance of our algorithm under different noise levels is assessed using receiver operating characteristic curves on simulated data. In addition, using the well-characterized visual motor network as grounds to test our model, we present the information flow obtained during a reaching task following left or right visual stimuli. These promising results present the transfer of information from the eyes to the primary motor cortex. The information flow obtained using our technique can also be projected back to the anatomy and animated to produce videos of the information path through the white matter, opening a new window into multi-modal dynamic brain connectivity

A cognitive prosthesis for complex decision-making

While simple heuristics can be ecologically rational and effective in naturalistic decision making contexts, complex situations require analytical decision making strategies, hypothesis-testing and learning. Sub-optimal decision strategies – using simplified as opposed to analytic decision rules – have been reported in domains such as healthcare, military operational planning, and government policy making. We investigate the potential of a computational toolkit called “IMAGE” to improve decision-making by developing structural knowledge and increasing understanding of complex situations. IMAGE is tested within the context of a complex military convoy management task through (a) interactive simulations, and (b) visualization and knowledge representation capabilities. We assess the usefulness of two versions of IMAGE (desktop and immersive) compared to a baseline. Results suggest that the prosthesis helped analysts in making better decisions, but failed to increase their structural knowledge about the situation once the cognitive prosthesis is removed

Mesure de champ électrique et de température par sonde électro-optique

International audienc

Mesure vectorielle de champs électriques microondes et de température par transducteurs électro-optiques

Refractive indices of electro-optic (EO) crystals (e.g. LiTaO3) have the particularity to be linearly dependent, via the Pockels' effect, on the magnitude of a unique component of an applied electric field. This nonlinear property makes those crystals good candidates to develop fully-dielectric made probes dedicated to non-invasive vectorial E-field measurements, as long as the E-field to be measured is strong enough. The poor sensitivity of those probes can be improved of several orders of magnitude using a Fabry-Pérot cavity. Unfortunately, the optical properties of the EO crystals depend also on the temperature involving temporal instability of the EO response of the probe under outdoor conditions.The EO transducer developed within the IMEP-LAHC laboratory, in association with the centre d'étude de Gramat, and described in this report, has permitted to perform the first simultaneous measurements of one E-field component and temperature with an accuracy of about 40 mK during several minutes under drastic experimental conditions. The EO transducer has a flat response over a bandwidth from quasi DC to 16 GHz, a spatial resolution of about 100 microns and selectivity better than 25 dB.Les cristaux électro-optiques (EO) comme le LiTaO3, présentent un indice de réfraction qui dépend linéairement, via l'effet Pockels, de l'amplitude d'une composante unique du champ électrique qui lui est appliqué, propriété qui permet de les utiliser comme détecteurs entièrement diélectriques, dédiés à la mesure vectorielle et non perturbative de champs électriques. Comme cette propriété est due à des effets non-linéaires, ces sondes EO possèdent des sensibilités (champ minimum mesurable) intrinsèquement faibles. Des sondes EO basées sur la modulation d'amplitude, utilisant une cavité Fabry-Pérot, permettent néanmoins d'améliorer cette sensibilité de plusieurs ordres de grandeur. Malheureusement les propriétés optiques de ces cristaux dépendent également de la température, engendrant une instabilité temporelle de la réponse EO de la sonde pour des mesures dites de «terrain». Le système développé au sein de l'IMEP-LAHC, en collaboration avec le centre d'étude de Gramat, et presenté dans ce manuscrit, a permis d'aboutir à la première mesure simultanée d'une composante du champ électrique et de la température avec une précision de l'ordre de 40 mK, et ce pendant plusieurs minutes dans des conditions expérimentales drastiques. Ce transducteur EO présente une réponse plate sur une bande spectrale allant du quasi DC à 16 GHz, une résolution spatiale d'une centaine de micron et une sélectivité supérieure à 25 dB