Drawing space : from early sketches to finished artwork : rsearch on a personal language through experimentation

This final work explores my obsession about space through personal practice. Its experimental nature seeks to open new paths, as well as overcome some limitations in the exercise of drawing, and focuses on the following topics: The quest for more sensitive means of spatial representations and solutions to evoke depth, perspective and movement other than the figurative techniques. Finding my own graphical and plastic language embedded into the physical and psychological experience of space, exploring other forms of creative and sensitive expression. The practical research project that was developed is also supported by a written part which includes a critical analysis of my work as well as an element of research on the Portuguese artist Nadir Afonso, and the Ethiopian born, New York based contemporary artist Julie Mehretu; both of whom´s work is deeply rooted into the expression of space, and their abstract languages convey a strong presence of physical reality whilst going beyond our visual perception of the world; characteristics in the representation of space which I find extremely interesting and justify my choice to study them. Furthermore, I thought that the fact their narrative and style are very different from each other would make for an interesting confrontation to explore. The result of my immersion in their work, and the process of finding within it references for my own personal development, allowed me to open up my mind to a new way of looking at space, giving me new means by which to express it, and helped me clarify some underlying paradoxes with which I’ve fought about the medium. At the same time it helped me refine my interest in the relationship between the man-made and Nature linked to a more metaphysical dimension. Overall the development of this project is a testimony of how I gained confidence to break out of my comfort zone, bringing the initial sketch into becoming a fully autonomous drawing, and how engaging into the abstract opened for me a door to a whole new plane in which I can translate feelings and emotions related to the experience of spac

Tunable source of correlated atom beams

We use a one-dimensional optical lattice to modify the dispersion relation of atomic matter waves. Four-wave mixing in this situation produces atom pairs in two well defined beams. We show that these beams present a narrow momentum correlation, that their momenta are precisely tunable, and that this pair source can be operated both in the regime of low mode occupancy and of high mode occupancy

Déposition d'électrolyte de type fluorite pour les SOFC en utilisant la projection de suspensions par plasma

Les électrolytes à base d'oxyde de cérium sont considérés depuis plus de 20 ans pour les applications aux piles à combustible à oxyde solide (SOFC). Il y a par contre quelques limitations que cette étude tente de résoudre. L'objectif de l'étude est de synthétiser une mince couche (50-100 µm) de CeO2 dopé à l'aide d'une suspension projetée dans du plasma. Les propriétés de CeO2 dopé avec des mélanges de dopant seront mesurées. Les mélanges seront faits de façon à ce que le rayon moyen soit le plus près possible du rayon ionique critique de l'oxyde de cérium. L'augmentation d'entropie de mélange permettra d'augmenter la quantité de dopant pouvant être introduits dans la matrice de CeO2 avant que les associations entre les défauts ne mènent à une chute de la conductivité ionique. Les électrolytes sont produits par pulvérisation d'une suspension (ou solution) dans un plasma supersonique. Cette méthode développée récemment par le CRTP doit d'abord être optimisée pour produire de fines couches d'électrolyte."--Résumé abrégé par UM

Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance

We report the experimental realization of a single-species atomic four-wave mixing process with BEC collisions for which the angular distribution of scattered atom pairs is not isotropic, despite the collisions being in the $s$-wave regime. Theoretical analysis indicates that this anomalous behavior can be explained by the anisotropic nature of the gain in the medium. There are two competing anisotropic processes: classical trajectory deflections due to the mean-field potential, and Bose enhanced scattering which bears similarity to super-radiance. We analyse the relative importance of these processes in the dynamical buildup of the anisotropic density distribution of scattered atoms, and compare to optically pumped super-radiance.Comment: 13 pages, 10 figures, added a fuller discussion of timescales, otherwise some minor changes in the text and the formatting of Figures 5-

An acoustic analog to the dynamical Casimir effect in a Bose-Einstein condensate

We have realized an acoustic analog to the Dynamical Casimir effect. The density of a trapped Bose-Einstein condensate is modulated by changing the trap stiffness. We observe the creation of correlated excitations with equal and opposite momenta, and show that for a well defined modulation frequency, the frequency of the excitations is half that of the trap modulation frequency.Comment: Includes supplemental informatio

The Bitcoin Brain Drain: Examining the Use and Abuse of Bitcoin Brain Wallets

In the cryptocurrency Bitcoin, users can deterministically derive the private keys used for transmitting money from a password. Such “brain wallets” are appealing because they free users from storing their private keys on untrusted computers. Unfortunately, they also enable attackers to conduct unlimited offline password guessing. In this paper, we report on the first large-scale measurement of the use of brain wallets in Bitcoin. Using a wide range of word lists, we evaluated around 300 billion passwords. Surprisingly, after excluding activities by researchers, we identified just 884 brain wallets worth around $100K in use from September 2011 to August 2015. We find that all but 21 wallets were drained, usually within 24 h but often within minutes. We find that around a dozen “drainers” are competing to liquidate brain wallets as soon as they are funded. We find no evidence that users of brain wallets loaded with more bitcoin select stronger passwords, but we do find that brain wallets with weaker passwords are cracked more quickly

Sub-Poissonian number differences in four-wave mixing of matter waves

We demonstrate sub-Poissonian number differences in four-wave mixing of Bose-Einstein condensates of metastable helium. The collision between two Bose-Einstein condensates produces a scattering halo populated by pairs of atoms of opposing velocities, which we divide into several symmetric zones. We show that the atom number difference for opposing zones has sub-Poissonian noise fluctuations whereas that of nonopposing zones is well described by shot noise. The atom pairs produced in a dual number state are well adapted to sub shot-noise interferometry and studies of Einstein-Podolsky-Rosen-type nonlocality tests.Comment: 4 pages, 3 figure

Application de règles de gestion à un système de fabrication : classification des objectifs atteints en vue de leur utilisation

Dans la suite, nous proposons deux méthodes utilisables pour classer les résultats obtenus en utilisant différentes règles pour gérer un système de production. L'objectif essentiel de ce travail est d'obtenir des classes de résultats qu'il est possible de qualifier et de représenter simplement