Análisis teórico del contacto plasma-superficie y sus aplicaciones industriales

Actualmente, la física de plasmas constituye una parte importante de la investigación en física que está siendo desarrollada. Su campo de aplicación varía desde el estudio de plasmas interestelares y cósmicos, como las estrellas, las nebulosas, el medio intergaláctico, etc.; hasta aplicaciones más terrenales como la producción de microchips o los dispositivos de iluminación. Resulta particularmente interesante el estudio del contacto de una superficie metálica con un plasma. Siendo la razón que, la dinámica de la interfase formada entre un plasma imperturbado y una superficie metálica, resulta de gran importancia cuando se trata de estudiar problemas como: la implantación iónica en una oblea de silicio, el grabado por medio de plasmas, la carga de una aeronave cuando atraviesa la ionosfera y la diagnosis de plasmas mediante sondas de Langmuir. El uso de las sondas de Langmuir está extendido a través de multitud de aplicaciones tecnológicas e industriales como método de diagnosis de plasmas. Algunas de estas aplicaciones han sido mencionadas justo en el párrafo anterior. Es más, su uso también es muy popular en la investigación en física de plasmas, por ser una de las pocas técnicas de diagnosis que proporciona información local sobre el plasma. El equipamiento donde es habitualmente implementado varía desde plasmas de laboratorio de baja temperatura hasta plasmas de fusión en dispositivos como tokamaks o stellerators. La geometría más popular de este tipo de sondas es cilíndrica, y la principal magnitud que se usa para diagnosticar el plasma es la corriente recogida por la sonda cuando se encuentra polarizada a un cierto potencial. Existe un interes especial en diagnosticar por medio de la medida de la corriente iónica recogida por la sonda, puesto que produce una perturbación muy pequeña del plasma en comparación con el uso de la corriente electrónica. Dada esta popularidad, no es de extrañar que grandes esfuerzos se hayan realizado en la consecución de un modelo teórico que explique el comportamiento de una sonda de Langmuir inmersa en un plasma. Hay que remontarse a la primera mitad del siglo XX para encontrar las primeras teorías que permiten diagnosticar parámetros del plasma mediante la medida de la corriente iónica recogida por la sonda de Langmuir. Desde entonces, las mejoras en estos modelos y el desarrollo de otros nuevos ha sido una constante en la investigación en física de plasmas. No obstante, todavía no está claro como los iones se aproximan a la superficie de la sonda. Las dos principales, a la par que opuestas, aproximaciones al problema que están ampliamente aceptadas son: la radial y la orbital; siendo el problema que ambas predicen diferentes valores para la corriente iónica. Los experimentos han arrojado resultados de acuerdo con ambas teorías, la radial y la orbital; y lo que es más importante, una transición entre ambos ha sido recientemente observada. La mayoría de los logros conseguidos a la hora de comprender como los iones caen desde el plasma hacia la superficie de la sonda, han sido llevados a cabo en el campo de la dinámica de fluidos o la teoría cinética. Por otra parte, este problema puede ser abordado mediante el uso de simulaciones de partículas. La principal ventaja de las simulaciones de partículas sobre los modelos de fluidos o cinéticos es que proporcionan mucha más información sobre los detalles microscópicos del movimiento de las partículas, además es relativamente fácil introducir interacciones complejas entre las partículas. No obstante, estas ventajas no se obtienen gratuitamente, ya que las simulaciones de partículas requieren grandísimos recursos. Por esta razón, es prácticamente obligatorio el uso de técnicas de procesamiento paralelo en este tipo de simulaciones. El vacío en el conocimiento de las sondas de Langmuir, es el que motiva nuestro trabajo. Nuestra aproximación, y el principal objetivo de este trabajo, ha sido desarrollar una simulación de partículas que nos permita estudiar el problema de una sonda de Langmuir inmersa en un plasma y que está negativamente polarizada con respecto a éste. Dicha simulación nos permitiría estudiar el comportamiento de los iones en los alrededores de una sonda cilíndrica de Langmuir, así como arrojar luz sobre la transición entre las teorías radiales y orbitales que ha sido observada experimentalmente. Justo después de esta sección introductoria, el resto de la tesis está dividido en tres partes tal y como sigue: La primera parte está dedicada a establecer los fundamentos teóricos de las sondas de Langmuir. En primer lugar, se realiza una introducción general al problema y al uso de sondas de Langmuir como método de diagnosis de plasmas. A continuación, se incluye una extensiva revisión bibliográfica sobre las diferentes teorías que proporcionan la corriente iónica recogida por una sonda. La segunda parte está dedicada a explicar los detalles de las simulaciones de partículas que han sido desarrolladas a lo largo de nuestra investigación, así como los resultados obtenidos con las mismas. Esta parte incluye una introducción sobre la teoría que subyace el tipo de simulaciones de partículas y las técnicas de paralelización que han sido usadas en nuestros códigos. El resto de esta parte está dividido en dos capítulos, cada uno de los cuales se ocupa de una de las geometrías consideradas en nuestras simulaciones (plana y cilíndrica). En esta parte discutimos también los descubrimientos realizados relativos a la transición entre el comportamiento radial y orbital de los iones en los alrededores de una sonda cilíndrica de Langmuir. Finalmente, en la tercera parte de la tesis se presenta un resumen del trabajo realizado. En este resumen, se enumeran brevemente los resultados de nuestra investigación y se han incluido algunas conclusiones. Después de esto, se enumeran una serie de perspectivas futuras y extensiones para los códigos desarrollados.

Neural fields with sigmoidal firing rates: approximate solutions

Many tissue level models of neural networks are written in the language of nonlinear integro-differential equations. Analytical solutions have only been obtained for the special case that the nonlinearity is a Heaviside function. Thus the pursuit of even approximate solutions to such models is of interest to the broad mathematical neuroscience community. Here we develop one such scheme, for stationary and travelling wave solutions, that can deal with a certain class of smoothed Heaviside functions. The distribution that smoothes the Heaviside is viewed as a fundamental object, and all expressions describing the scheme are constructed in terms of integrals over this distribution. The comparison of our scheme and results from direct numerical simulations is used to highlight the very good levels of approximation that can be achieved by iterating the process only a small number of times.

As redes sociais e a participação política no âmbito do marketing político do Governo Federal Brasileiro entre 2011 e 2014 : atuação do Ministério da Educação no Facebook

A democracia contemporânea vem, ao longo das últimas décadas, recebendo cada vez mais influência dos meios de comunicação em seus processos. Com o surgimento e propagação da Internet, os governos tem precisado se adaptar e se preocupar com a transparência de suas ações e com as inúmeras vozes de atores sociais cada vez mais conectados, informados e munidos de ferramentas, por meio das quais, podem realizar comunicações de grande alcance de forma rápida e eficaz, sem o intermédio de grandes meios de comunicação. Com o objetivo de observar a relação entre o governos e cidadãos por meio das redess sociais online – um dos principais meios por onde a sociedade, hoje, tem se comunicado e se mobilizado sobre inúmeras, inclusive, políticas – esse estudo analisou como o Ministério da Educação do Brasil (MEC), órgão responsável pelo planejamento e desenvolvimento de políticas públicas para educação no país, trabalha sua comunicação com o cidadão por meio do Facebook e como utiliza essa ferramenta no processo de implementação e avaliação de suas políticas. O trabalho foi realizado por meio do estudo exploratório e da análise qualitativa dos dados colhidos na página MEC no Facebook entre anos de 2011 e 2014, período do primeiro mandato da presidente Dilma Rousseff. Com a análise, observou-se que o MEC modificou bastante a forma como se comunica por esta rede social, recebendo, inclusive, aparente melhor infra-estrutura para esta tarefa. Sua mudança de postura no Facebook deixa claro o interesse e a busca pela participação dos cidadadãos no desevolvimento de suas políticas públicas. Por outro lado, mostra que essa participação é, de certa forma, limitada pela atitude do MEC de não desenvolver diálogo com o cidadão, mantendo-os sempre a certa distância.

A pesca do bacalhau durante o período do Estado Novo (1933-1974) : contributo para as relações interculturais

A presente dissertação tem como objeto de estudo a pesca do bacalhau feita por portugueses sob a bandeira de Portugal durante o período do Estado Novo (1933-1974). Investigou-se as razões para um investimento e um protecionismo tão forte à indústria da pesca do bacalhau. É indissociável do estudo da demanda portuguesa por este peixe, à época muito abundante no noroeste atlântico, as políticas autárcicas e de subsistência pilares da economia do Estado Novo, assim como a implantação e robustecimento da Instituição Corporativa. Subjacente a estas linhas de matriz económica mas paradigmáticas do novo regime, estava também a reconstrução da identidade portuguesa, a sacralização do trabalho e a heroicidade do pescador português do bacalhau. A existência da tentativa de revivificação da glória dos descobrimentos na pesca do bacalhau. A criação de um ambiente social, político e religioso que levaram à persecução destas políticas e consequentemente do engrandecimento da estrutura do Estado Novo, resultando até na sedimentação de apoio popular. O desenvolvimento da frota de pesca longínqua foi quase uma única janela de oportunidades para o conhecimento de novos mundos. A montante e a jusante da atividade piscatória também se desenvolveram indústrias e comércio internacional. A participação em organizações internacionais de regulação das pescas proporcionou contatos Institucionais com outras nações, não raro utilizados para quebrar isolamentos e propagandear o Estado Novo e as suas manifestações culturais e identitárias que suscitaram relacionamentos interculturais. Para além destes contatos mais formais, também se desenvolveram contatos informais, que se repercutiram na criação e manifestação de conhecimento mútuo e claro de condições para a gestação da interculturidade. Estes desenvolvimentos de relações informais, de contatos profissionais também geraram relações culturais que se manifestaram em projetos individuais de vida associados às migrações.

O SIVICC como um sistema dissuasor da ilicitude e de apoio à atividade operacional da GNR

O objeto de estudo da presente investigação é o SIVICC. Sendo o objetivo geral demonstrar o seu desempenho organizacional nos domínios da dissuasão da ilicitude, do apoio à decisão e do suporte à atividade operacional da GNR, procurando adicionar e aprofundar conhecimento teórico e empírico. Em termos de metodologia optámos por uma estratégia de investigação qualitativa e relativamente ao desenho da pesquisa optou-se pela transversal. Os métodos e técnicas utilizadas foram as entrevistas semiestruturadas com a respetiva análise de conteúdo e a análise documental. Como resultado principal destacamos que, com base numa doutrina assente em princípios centrados em rede e no empirismo resultante das entrevistas efetuadas, o SIVICC proporciona superioridade de informação resultando numa consciência situacional partilhada da organização, o que conduz a melhores efeitos operacionais, que contribuem na prossecução da segurança de Portugal e da UE, através de uma efetiva vigilância diária e controlo do mar territorial e zona costeira. Concluímos que o SIVICC promove um apoio importante na tomada de decisão e suporta eficazmente e eficientemente a atividade operacional da GNR, que se vai refletir numa vantagem competitiva sobre o adversário que é persuadido a mudar os seus comportamentos através da dissuasão que o sistema proporciona. Abstract: The study object of this research is the SIVICC. The overall goal is to prove their organizational performance in the areas of deterrence of unlawful, in decision support and in supporting the operational activities of the GNR, attempting to add and deepen theoretical and empirical knowledge. In terms of methodology we chose a qualitative research strategy and for the design of research we chose the transversal. The methods and techniques used were semi-structured interviews with the respective content analysis and document analysis. The main result we highlight, based on a doctrine sustained on principles of centered network operations and a result empiricism of conducted interviews, that the SIVICC provides information superiority resulting in a shared situational awareness of the organization, leading to better operational effects that contribute to the pursuit security in Portugal and in the EU, through effective daily monitoring and control of the territorial sea and coastal zone. We conclude that the SIVICC promotes an important support decision making and supports effectively and efficiently operational activity of the GNR, which will reflect a competitive advantage over the adversary who is persuaded to change their behavior through deterrence that the system provides.

La compra de pintura por parte del maestro de obra: elementos cognitivos, afectivos, conductuales y de entorno

RESUMEN: A pesar del posicionamiento que la marca Pintuco tiene entre los consumidores, su participación en el mercado nacional viene cayendo en los últimos años. El presente trabajo aporta elementos para mejorar esta situación por medio de una mayor fidelización de los maestros de obra, en su calidad de influenciadores del proceso de compra de pintura. El objetivo de este trabajo es identificar los factores que influyen en este proceso y la relación que el maestro de obra tiene con la pintura a nivel cognitivo, afectivo, conductual y de entorno, usando técnicas como las metáforas de Zaltman, la cadena de medios y fines, y la observación etnográfica. El trabajo muestra que el maestro de obra se ve a sí mismo como un artista y un experto deseoso de compartir sus conocimientos con sus compañeros y ayudantes. También se identificaron los principales valores asociados a la pintura y a la labor de pintar, tales como el reconocimiento por parte de los clientes, la credibilidad, y la estabilidad para su familia al conseguir más clientes. Finalmente se vio un alto interés por el precio en el punto de venta. Es así como se proponen en tres estrategias para fidelizar a este grupo en torno a su experticia y necesidad de reconocimiento, estabilidad familiar y credibilidad: La Escuela del Maestro Pintuco, el plan de Maestro Recomendado Pintuco, y los Puntos de Venta Certificados Pintuco.

Estética do apocalipse: (re) considerações acerca da (des) arborização urbana de Natal e seu contributo à saúde pública

This study intends to establish a relation between environmental degradation, particularly the devastation of the green canopy, and public health. Utilizing a mapping of the trees included in the researched area, each individual tree was analyzed according to its age, taxonomic listing, architecture, shape and size (determined by aesthetic/convenience reasons or deformed by pruning). Initially investigated were the covert reasons lying underneath the constant aggression against trees (which many times seem to contain elements of hatred and contempt) within the urban environment. In addition to that, the aspects concerning environmental modifications and the consequent impact on public health were also assessed. Two main problems promptly emerged as a result of the removal of trees: a) without a canopy to protect the areas, they became subject to winds directly blown from SW Africa and impregnated with aerosol partic les, which are common causes for respiratory disorders and, b) direct UV solar radiation, which causes some types of skin cancers and eye disorders. To reach such results, we studied the origins and formation of UV radiation induced cancers and searched for the UV radiation spectra of action, e.g., usual intensity and quantity reaching clear and shadowed spaces in a certain area and its consequences. In a second instance, we also searched for pertinent data resources in order to confirm the increase of skin cancer cases due to exposure to UV radiation and the relation between the destruction of the green canopy and the above mentioned problems. We believe that a few significant results have been achieved by this study, namely: the relation between a culture based on medieval beliefs and its consequences on the environment; how this culture exploits and deforms nature in pursuit of financial and psychological interests to a point of transforming the landscape into a copy of something devoid of any relation to latitude and altitude; and above all, the indifference concerning the alarming results carried by these modifications

Leitora-criadora: a experiência situada na construção dramatúrgica

This study has the purpose of investigating the term reader-creator , on the textual aspects of the dramatical works A Morte nos Olhos , A Memória Ferida and Na Outra Margem (2010) by Antonia Pereira Bezerra. In this sense, we propose an analysis of these works based on author‟s life experience as creative matter for a autofictional narrative, highlighting the relations between the autobiographical elements (LEJEUNE, 2008; DOSSE, 2009) and fictional elements in the construction of dramatic narratives. The theoretical analysis pervades the studies fields of Reception Aesthetics (ISER, 1996), memory (RICOUER, 2007) and narrative (RICOEUR, 2010), evidencing the relation between the author and the pursuit of her memories and life experiences, the matter to elaboration of writing. Then we intend thinking a reader-creator of herself, that at the same time she seeks in her memories the biographic aspects to her narrative, she converts this reality with the insertion of fictional elements from the imagination (SARTRE, 2008)

Evasão na educação profissional : estudo de caso de estudantes com necessidades específicas no Campus Taguatinga do Instituto Federal de Brasília

Dissertação apresentada para obtenção do grau de mestre do Mestrado em Educação Social e Intervenção Comunitária da Escola Superior de Educação do Instituto Politécnico de Santarém

Anorexia no masculino: Dinâmica e identificação

Dissertação de Mestrado apresentada no ISPA – Instituto Universitário para obtenção de grau de Mestre na especialidade de Psicologia Clínica

Evasão na educação profissional : estudo de caso de estudantes com necessidades específicas no Campus Taguatinga do Instituto Federal de Brasília

Dissertação apresentada para obtenção do grau de mestre do Mestrado em Educação Social e Intervenção Comunitária da Escola Superior de Educação do Instituto Politécnico de Santarém

Turning conflict into coexistence: cross-cutting ties and institutions in the agro-pastoral borderlands of Lake Naivasha basin, Kenya

The Maasai/Kikuyu agro-pastoral borderlands of Maiella and Enoosupukia, located in the hinterlands of Lake Naivasha’s agro-industrial hub, are particularly notorious in the history of ethnicised violence in the Kenya’s Rift Valley. In October 1993, an organised assault perpetrated by hundreds of Maasai vigilantes, with the assistance of game wardens and administration police, killed more than 20 farmers of Kikuyu descent. Consequently, thousands of migrant farmers were violently evicted from Enoosupukia at the instigation of leading local politicians. Nowadays, however, intercommunity relations are surprisingly peaceful and the cooperative use of natural resources is the rule rather than the exception. There seems to be a form of reorganization. Violence seems to be contained and the local economy has since recovered. This does not mean that there is no conflict, but people seem to have the facility to solve them peacefully. How did formerly violent conflicts develop into peaceful relations? How did competition turn into cooperation, facilitating changing land use? This dissertation explores the value of cross-cutting ties and local institutions in peaceful relationships and the non-violent resolution of conflicts across previously violently contested community boundaries. It mainly relies on ethnographic data collected between 2014 and 2015. The discussion therefore builds on several theoretical approaches in anthropology and the social sciences – that is, violent conflicts, cross-cutting ties and conflicting loyalties, joking relationships, peace and nonviolence, and institutions, in order to understand shared spaces that are experiencing fairly rapid social and economic changes, and characterised by conflict and coexistence. In the researched communities, cross-cutting ties and the split allegiances associated with them result from intermarriages, land transactions, trade, and friendship. By institutions, I refer to local peace committees, an attempt to standardise an aspect of customary law, and Nyumba Kumi, a strategy of anchoring community policing at the household level. In 2010, the state “implanted” these grassroots-level institutions and conferred on them the rights to handle specific conflicts and to prevent crime. I argue that the studied groups utilise diverse networks of relationships as adaptive responses to landlessness, poverty, and socio-political dynamics at the local level. Material and non-material exchanges and transfers accompany these social and economic ties and networks. In addition to being instrumental in nurturing a cohesive social fabric, I argue that such alliances could be thought of as strategies of appropriation of resources in the frontiers – areas that are considered to have immense agricultural potential and to be conducive to economic enterprise. Consequently, these areas are continuously changed and shaped through immigration, population growth, and agricultural intensification. However, cross-cutting ties and intergroup alliances may not necessarily prevent the occurrence or escalation of conflicts. Nevertheless, disputes and conflicts, which form part of the social order in the studied area, create the opportunities for locally contextualised systems of peace and non-violence that inculcate the values of cooperation, coexistence, and restraint from violence. Although the neo-traditional institutions (local peace committees and Nyumba Kumi) face massive complexities and lack the capacity to handle serious conflicts, their application of informal constraints in dispute resolution provides room for some optimism. Notably, the formation of ties and alliances between the studied groups, and the use of local norms and values to resolve disputes, are not new phenomena – they are reminiscent of historical patterns. Their persistence, particularly in the context of Kenya, indicates a form of historical continuity, which remains rather “undisturbed” despite the prevalence of ethnicised political economies. Indeed, the formation of alliances, which are driven by mutual pursuit of commodities (livestock, rental land, and agricultural produce), markets, and diversification, tends to override other identities. While the major thrust of social science literature in East Africa has focused on the search for root causes of violence, very little has been said about the conditions and practices of cooperation and non-violent conflict resolution. In addition, situations where prior violence turned into peaceful interaction have attracted little attention, though the analysis of such transitional phases holds the promise of contributing to applicable knowledge on conflict resolution. This study is part of a larger multidisciplinary project, “Resilience in East African Landscapes” (REAL), which is a Marie Curie Actions Innovative Training Networks (ITN) project. The principal focus of this multidisciplinary project is to study past, present, and future thresholds and sustainable trajectories in human-landscape interactions in East Africa over the last millennia. While other individual projects focus on long-term ecosystem dynamics and societal interactions, my project examines human-landscape interactions in the present and the very recent past (i.e. the period in which events and processes were witnessed or can still be recalled by today’s population). The transition from conflict to coexistence and from competition to cooperative use of previously violently contested land resources is understood here as enhancing adaptation in the face of social-political, economic, environmental, and climatic changes. This dissertation is therefore a contribution to new modes of resilience in human-landscape interactions after a collapse situation.

Essays on employment / education, investment in education and student achievement

Méthodologie: Modèle de régression quantile de variable instrumentale pour données de Panel utilisant la fonction de production partielle

Applications of perceptual sparse representation (Spikegram) for copyright protection of audio signals

Chaque année, le piratage mondial de la musique coûte plusieurs milliards de dollars en pertes économiques, pertes d’emplois et pertes de gains des travailleurs ainsi que la perte de millions de dollars en recettes fiscales. La plupart du piratage de la musique est dû à la croissance rapide et à la facilité des technologies actuelles pour la copie, le partage, la manipulation et la distribution de données musicales [Domingo, 2015], [Siwek, 2007]. Le tatouage des signaux sonores a été proposé pour protéger les droit des auteurs et pour permettre la localisation des instants où le signal sonore a été falsifié. Dans cette thèse, nous proposons d’utiliser la représentation parcimonieuse bio-inspirée par graphe de décharges (spikegramme), pour concevoir une nouvelle méthode permettant la localisation de la falsification dans les signaux sonores. Aussi, une nouvelle méthode de protection du droit d’auteur. Finalement, une nouvelle attaque perceptuelle, en utilisant le spikegramme, pour attaquer des systèmes de tatouage sonore. Nous proposons tout d’abord une technique de localisation des falsifications (‘tampering’) des signaux sonores. Pour cela nous combinons une méthode à spectre étendu modifié (‘modified spread spectrum’, MSS) avec une représentation parcimonieuse. Nous utilisons une technique de poursuite perceptive adaptée (perceptual marching pursuit, PMP [Hossein Najaf-Zadeh, 2008]) pour générer une représentation parcimonieuse (spikegramme) du signal sonore d’entrée qui est invariante au décalage temporel [E. C. Smith, 2006] et qui prend en compte les phénomènes de masquage tels qu’ils sont observés en audition. Un code d’authentification est inséré à l’intérieur des coefficients de la représentation en spikegramme. Puis ceux-ci sont combinés aux seuils de masquage. Le signal tatoué est resynthétisé à partir des coefficients modifiés, et le signal ainsi obtenu est transmis au décodeur. Au décodeur, pour identifier un segment falsifié du signal sonore, les codes d’authentification de tous les segments intacts sont analysés. Si les codes ne peuvent être détectés correctement, on sait qu’alors le segment aura été falsifié. Nous proposons de tatouer selon le principe à spectre étendu (appelé MSS) afin d’obtenir une grande capacité en nombre de bits de tatouage introduits. Dans les situations où il y a désynchronisation entre le codeur et le décodeur, notre méthode permet quand même de détecter des pièces falsifiées. Par rapport à l’état de l’art, notre approche a le taux d’erreur le plus bas pour ce qui est de détecter les pièces falsifiées. Nous avons utilisé le test de l’opinion moyenne (‘MOS’) pour mesurer la qualité des systèmes tatoués. Nous évaluons la méthode de tatouage semi-fragile par le taux d’erreur (nombre de bits erronés divisé par tous les bits soumis) suite à plusieurs attaques. Les résultats confirment la supériorité de notre approche pour la localisation des pièces falsifiées dans les signaux sonores tout en préservant la qualité des signaux. Ensuite nous proposons une nouvelle technique pour la protection des signaux sonores. Cette technique est basée sur la représentation par spikegrammes des signaux sonores et utilise deux dictionnaires (TDA pour Two-Dictionary Approach). Le spikegramme est utilisé pour coder le signal hôte en utilisant un dictionnaire de filtres gammatones. Pour le tatouage, nous utilisons deux dictionnaires différents qui sont sélectionnés en fonction du bit d’entrée à tatouer et du contenu du signal. Notre approche trouve les gammatones appropriés (appelés noyaux de tatouage) sur la base de la valeur du bit à tatouer, et incorpore les bits de tatouage dans la phase des gammatones du tatouage. De plus, il est montré que la TDA est libre d’erreur dans le cas d’aucune situation d’attaque. Il est démontré que la décorrélation des noyaux de tatouage permet la conception d’une méthode de tatouage sonore très robuste. Les expériences ont montré la meilleure robustesse pour la méthode proposée lorsque le signal tatoué est corrompu par une compression MP3 à 32 kbits par seconde avec une charge utile de 56.5 bps par rapport à plusieurs techniques récentes. De plus nous avons étudié la robustesse du tatouage lorsque les nouveaux codec USAC (Unified Audion and Speech Coding) à 24kbps sont utilisés. La charge utile est alors comprise entre 5 et 15 bps. Finalement, nous utilisons les spikegrammes pour proposer trois nouvelles méthodes d’attaques. Nous les comparons aux méthodes récentes d’attaques telles que 32 kbps MP3 et 24 kbps USAC. Ces attaques comprennent l’attaque par PMP, l’attaque par bruit inaudible et l’attaque de remplacement parcimonieuse. Dans le cas de l’attaque par PMP, le signal de tatouage est représenté et resynthétisé avec un spikegramme. Dans le cas de l’attaque par bruit inaudible, celui-ci est généré et ajouté aux coefficients du spikegramme. Dans le cas de l’attaque de remplacement parcimonieuse, dans chaque segment du signal, les caractéristiques spectro-temporelles du signal (les décharges temporelles ;‘time spikes’) se trouvent en utilisant le spikegramme et les spikes temporelles et similaires sont remplacés par une autre. Pour comparer l’efficacité des attaques proposées, nous les comparons au décodeur du tatouage à spectre étendu. Il est démontré que l’attaque par remplacement parcimonieux réduit la corrélation normalisée du décodeur de spectre étendu avec un plus grand facteur par rapport à la situation où le décodeur de spectre étendu est attaqué par la transformation MP3 (32 kbps) et 24 kbps USAC.

The dehydrogenation reactions between LiH and organic amines for solid state hydrogen storage systems

Hydrogen is considered as an appealing alternative to fossil fuels in the pursuit of sustainable, secure and prosperous growth in the UK and abroad. However there exists a persisting bottleneck in the effective storage of hydrogen for mobile applications in order to facilitate a wide implementation of hydrogen fuel cells in the fossil fuel dependent transportation industry. To address this issue, new means of solid state chemical hydrogen storage are proposed in this thesis. This involves the coupling of LiH with three different organic amines: melamine, urea and dicyandiamide. In principle, thermodynamically favourable hydrogen release from these systems proceeds via the deprotonation of the protic N-H moieties by the hydridic metal hydride. Simultaneously hydrogen kinetics is expected to be enhanced over heavier hydrides by incorporating lithium ions in the proposed binary hydrogen storage systems. Whilst the concept has been successfully demonstrated by the results obtained in this work, it was observed that optimising the ball milling conditions is central in promoting hydrogen desorption in the proposed systems. The theoretical amount of 6.97 wt% by dry mass of hydrogen was released when heating a ball milled mixture of LiH and melamine (6:1 stoichiometry) to 320 °C. It was observed that ball milling introduces a disruption in the intermolecular hydrogen bonding network that exists in pristine melamine. This effect extends to a molecular level electron redistribution observed as a function of shifting IR bands. It was postulated that stable phases form during the first stages of dehydrogenation which contain the triazine skeleton. Dehydrogenation of this system yields a solid product Li2NCN, which has been rehydrogenated back to melamine via hydrolysis under weak acidic conditions. On the other hand, the LiH and urea system (4:1 stoichiometry) desorbed approximately 5.8 wt% of hydrogen, from the theoretical capacity of 8.78 wt% (dry mass), by 270 °C accompanied by undesirable ammonia and trace amount of water release. The thermal dehydrogenation proceeds via the formation of Li(HN(CO)NH2) at 104.5 °C; which then decomposes to LiOCN and unidentified phases containing C-N moieties by 230 °C. The final products are Li2NCN and Li2O (270 °C) with LiCN and Li2CO3 also detected under certain conditions. It was observed that ball milling can effectively supress ammonia formation. Furthermore results obtained from energetic ball milling experiments have indicated that the barrier to full dehydrogenation between LiH and urea is principally kinetic. Finally the dehydrogenation reaction between LiH and dicyandiamide system (4:1 stoichiometry) occurs through two distinct pathways dependent on the ball milling conditions. When ball milled at 450 RPM for 1 h, dehydrogenation proceeds alongside dicyandiamide condensation by 400 °C whilst at a slower milling speed of 400 RPM for 6h, decomposition occurs via a rapid gas desorption (H2 and NH3) at 85 °C accompanied by sample foaming. The reactant dicyandiamide can be generated by hydrolysis using the product Li2NCN.