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Multi-factor authentication is a term that was foreign until a few years ago. But in reality, it has been around for decades in the world of computer security. In theory, has the purpose to improve the security of user authentication by adding an extra layer of security to the process. Although password authentication has been shown to be an imperfect technique, it is still the most widely used today. That is why this research has been carried out, to shed light on the issue of why multi-factor authentication is not a fundamental pillar in security. For this, two promising protocols of the second authentication factor have been chosen, Time-based One-time Password (TOTP) and Universal 2nd Factor (U2F), and the usability of these methods has been compared together with password authentication usability as well. A Systematic Literature Review has been executed to answer the raised research question. Although the setup and login processes of the protocols are excessively slow, the results show that the U2F devices are overall more usable than TOTP, as they have a more “friendly” daily usage. But not enough data has been found on TOTP to be able to make a comparison with a solid basis. / La autenticación de múltiples factores es un término que era extraño hasta hace varios años. Pero en realidad, ha existido durante décadas en el mundo de la seguridad informática. En teoría, su objetivo es mejorar la seguridad del proceso de autenticación de usuarios, agregando una capa adicional de seguridad al proceso. Aunque se ha demostrado que la autenticación de contraseña es una técnica imperfecta, sigue siendo la más utilizada en la actualidad. Esta es la razón por la que se ha realizado esta investigación, para arrojar luz sobre el tema de por qué la autenticación de múltiples factores no es un pilar fundamental en la seguridad. Para ello, se han elegido dos protocolos prometedores del segundo factor de autentificación, como son, Time-based One-time Password (TOTP) y Universal 2nd Factor (U2F), y se ha comparado la usabilidad de estos métodos junto con usabilidad de la autenticación por contraseña. Se ha realizado una Revisión Sistemática de la Literatura (Systematic Literature Review) para dar respuesta a la pregunta de investigación planteada. Aunque los procesos de configuración e inicio de sesión de los protocolos son excesivamente lentos, los resultados muestran que los dispositivos U2F son en general mas usables ya que tienen un uso diario más “amigable”. Pero no se han encontrado suficientes datos sobre TOTP para poder hacer una comparación con una sólida base. / <p><strong>Laburpena</strong> [Summary/Abstract, Basque/baskiska]</p><p>Faktore-anitzeko autentifikazioa orain dela urte gutxi arte arrotza izan den terminoetako bat da. Baina, egia esan, hamarkada batzuk daramatza segurtasun informatikoaren munduan errotua. Teorian, erabiltzaileen autentifikazio-prozesuaren segurtasuna hobetzeko helburu du, prozesuari segurtasun-geruza berri bat gehituz. Pasahitz autentifikazio teknika inperfektua dela frogatu bada ere, gaur egun oraindik erabiliena da. Horregatik egin da ikerketa hau, faktore anitzeko autentifikazioa zergatik ez den segurtasunaren oinarrizko zutabea argitzeko. Horretarako, faktore-anitzeko autentifikazio barruan aurkitzen diren bi protokolo itxaropentsu aukeratu dira, hala nola, Time-based One-time Password (TOTP) eta Universal 2nd Factor (U2F), eta hauen erabilgarritasuna konparatu da pasahitz bidezko erabilgarritasunarekin batera. Planteatutako ikerketa galderari erantzuteko Literatura Ikerketa Sistematikoa (Systematic Literature Review) burutu da, protokolo bakoitzaren onurak/eragozpenak bilduz eta hauen arteko konparaketa bat eginez. Protokoloen konfigurazio eta saioa hasteko prosezuak motelegiak badira ere, emaitzek erakusten dute U2F gailuak orokorreak TOTP baino erabilgarriagoak direla, eguneroko erabilera “lagunartekoagoa” baitute. Baina ez da datu nahikorik aurkitu TOTP-en oinarri sendo batekin konparazio bat egin ahal izateko.</p><p><strong>HITZ-GAKOAK:</strong> autentifikazioa, faktore-anitzeko autentifikazioa, Universal 2nd Factor, U2F, Time-based One-time Password, TOTP, alderaketa, erabilgarritasuna</p>

There are three main results in this dissertation. The first result is the construction of an abstract visual space for rational numbers mod1, based on the visual primitives, colour, and rational radial direction. Mathematics is performed in this visual notation by defining increasingly refined visual objects from these primitives. In particular, the existence of the Farey tree enumeration of rational numbers mod1 is identified in the texture of a two-dimensional animation. ¶ The second result is a new enumeration of the rational numbers mod1, obtained, and expressed, in abstract visual space, as the visual object coset waves of coset fans on the torus. Its geometry is shown to encode a countably infinite tree structure, whose branches are cosets, nZ+m, where n, m (and k) are integers. These cosets are in geometrical 1-1 correspondence with sequences kn+m, (of denominators) of rational numbers, and with visual subobjects of the torus called coset fans. ¶ The third result is an enumeration in time of the visual hierarchy of the discrete buds of the Mandelbrot boundary by coset waves of coset fans. It is constructed by embedding the circular Farey tree geometrically into the empty internal region of the Mandelbrot set. In particular, coset fans attached to points of the (internal) binary tree index countably infinite sequences of buds on the (external) Mandelbrot boundary.

Through creative and theoretical research, this practice-led PhD project investigates the conditions that facilitate embodied sensory awareness within digital inter-media installation. Central to this exploration are questions concerning ‘immersion.’ The research uses this term to describe a transformation in perception that allows us to shake off representational and symbolic meaning in favour of embodied, sensory and intuitive awareness within an installation space. Drawing from embodied memories of immersion in natural and spiritual environments, I consider the elements that contributed to these experiences and ask whether it is possible to create this sense of immersion in art. I then consider the elements that produce immersive, inter-media environments including space, sound, light, and projected moving images. Drawing on theoretical and artistic precedents, I propose a set of principles for producing a sense of embodied sensory immersion. The practical outcomes of the research - three digital inter-media installations included in the exhibition, in an other light - incorporate different combinations and treatments of these material elements to investigate and test the proposed principles.

Les végétaux, contrairement aux animaux, génèrent la plupart de leurs organes et tissus au cours de leur développement post-embryonnaire et ce, grâce à des tissus contenant de petits amas de cellules souches appelés méristèmes. Le méristème apical caulinaire (MAC), situé à l’extrémité de la tige, génère toute la partie aérienne de la plante. A sa périphérie, les organes latéraux (fleurs ou feuilles) sont générés selon un patron spatio-temporel précis appelé phyllotaxie. De nombreuses données accumulées ces 20 dernières années ont démontré qu’une hormone végétale, l’auxine, joue un rôle prépondérant dans le contrôle du devenir des cellules dans le MAC. Un ensemble de données expérimentales couplées à des modèles mathématiques suggère que l’auxine s’accumule successivement dans les sites d’organogenèse grâce à l’auto-organisation de ses transporteurs membranaires et instruit les cellules à se différencier en organes.Fautes d’outils appropriés, il était impossible jusqu’alors de visualiser l’auxine in vivo et d’étudier sa dynamique temporelle. Nous avons généré un nouveau senseur de la signalisation de l’auxine, appelé DII-Venus, qui permet de visualiser de manière indirecte mais spécifique les niveaux relatifs d’auxine in planta avec une excellente résolution spatio-temporelle. Cet outil a permis de mettre en évidence pour la première fois des oscillations circadiennes d’auxine au niveau du MAC. Une analyse complète de la structure de la voie de réponse transcriptionelle à l’auxine, couplée à des approches de modélisation, a permis de mettre en évidence des propriétés « tampon » de la voie transcriptionnelle qui la rendent relativement insensible aux fluctuations d’auxine, et contribuent à la robustesse du programme organogénétique. En revanche, la voie non-transriptionnelle de réponse à l’auxine, sensible à ces oscillations, génère des rythmicités de croissance au niveau du MAC qui contribuent à déterminer la temporalité de l’émergence de nouveaux organes. Ces résultats démontrent ainsi pour la première fois que la rythmicité de l’émergence de nouveaux organes au niveau du MAC n’est pas uniquement une conséquence des capacités d’auto-organisation du tissu mais est aussi contrôlée, au moins partiellement, par une horloge biologique. / Plants, contrarily to animals, are able to generate new organs and tissues throughout their lives thanks to the activity of specialized tissues containing stem cells called meristems. The shoot apical meristem (SAM), located at the shoot tip, generates all the aerial parts of the plant that arise after germination. At its periphery, organ production occurs following precise spatio-temporal patterns also known as phyllotaxis. During the past twenty years, the phytohormone auxin has been demonstrated to play a major role in this process. Indeed, both experimental and theoretical studies strongly suggest that auxin accumulates successively in sites of organogenesis thanks to its efflux carriers, and instructs cells to differentiate into organs.However, so far, very little is known about the actual temporal dynamics of auxin in tissues, because of the lack of appropriate tool to visualize auxin in vivo. We developed a new auxin signaling sensor, called DII-VENUS, that allows for monitoring auxin levels in planta with a good spatio-temporal resolution. Using this new tool, we were able to demonstrate that for the first time that the SAM is subjected to circadian oscillations of auxin levels. Our data suggest that these oscillations are not perceived by the auxin transcriptional pathway, which is predicted, according to our mathematical models, to exhibit buffering properties. However, they are perceived by the non-transcriptional putative receptor ABP1 and translated into rhythmic growth patterns at the SAM. These growth oscillations seem to regulate organ initiation in the meristem thus demonstrating for the first time the rhythmic emergence of organs at the SAM does not only result from the self-organizing properties of the tissue but is also controlled, at least partially, by a biological clock.

A scheme for Built-in-Self-Test (BIST) of analog signals with minimal area overhead, for measuring on-chip voltages in an all-digital manner is presented in this thesis. With technology scaling, the inverter switching times are becoming shorter thus leading to better resolution of edges in time. This time resolution is observed to be superior to voltage resolution in the face of reducing supply voltage and increasing variations as physical dimensions shrink. In this thesis, a new method of observability of analog signals is proposed, which is digital-friendly and scalable to future deep sub-micron (DSM) processes. The low-bandwidth analog test voltage is captured as the delay between a pair of clock signals. The delay thus setup is measured digitally in accordance with the desired resolution. Such an approach lends itself easily to distributed manner, where the routing of analog signals over long paths is minimized. A small piece of circuitry, called sampling head (SpH) placed near each test voltage, acts as a transducer converting the test voltage to a delay between a pair of low-frequency clocks. A probe clock and a sampling clock is routed serially to the sampling heads placed at the nodes of analog test voltages. This sampling head, present at each test node consists of a pair of delay cells and a pair of flip-flops, giving rise to as many sub-sampled signal pairs as the number of nodes. To measure a certain analog voltage, the corresponding sub-sampled signal pair is fed to a Delay Measurement Unit (DMU) to measure the skew between this pair. The concept is validated by designing a test chip in UMC 130 nm CMOS process. Sub-mV accuracy for static signals is demonstrated for a measurement time of few milliseconds and ENOB of 5.29 is demonstrated for low bandwidth signals in the absence of sample-and-hold circuitry. The sampling clock is derived from the probe clock using a PLL and the design equations are worked out for optimal performance. To validate the concept, the duty-cycle of the probe clock, whose ON-time is modulated by a sine wave, is measured by the same DMU. Measurement results from FPGA implementation confirm 9 bits of resolution.