Analysis and implementation of a multi-ratio switched capacitor DC-DC converter for a supercapacitor power supply

An energy harvesting system requires an energy storing device to store the energy retrieved from the surrounding environment. This can either be a rechargeable battery or a supercapcitor. Due to the limited lifetime of rechargeable batteries, they need to be periodically replaced. Therefore, a supercapacitor, which has ideally a limitless number of charge/discharge cycles can be used to store the energy; however, a voltage regulator is required to obtain a constant output voltage as the supercapacitor discharges. This can be implemented by a Switched-Capacitor DC-DC converter which allows a complete integration in CMOS technology, although it requires several topologies in order to obtain a high efficiency. This thesis presents the complete analysis of four different topologies in order to determine expressions that allow to design and determine the optimum input voltage ranges for each topology. To better understand the parasitic effects, the implementation of the capacitors and the non-ideal effect of the switches, in 130 nm technology, were carefully studied. With these two analysis a multi-ratio SC DC-DC converter was designed with an output power of 2 mW, maximum efficiency of 77%, and a maximum output ripple, in the steady state, of 23 mV; for an input voltage swing of 2.3 V to 0.85 V. This proposed converter has four operation states that perform the conversion ratios of 1/2, 2/3, 1/1 and 3/2 and its clock frequency is automatically adjusted to produce a stable output voltage of 1 V. These features are implemented through two distinct controller circuits that use asynchronous time machines (ASM) to dynamically adjust the clock frequency and to select the active state of the converter. All the theoretical expressions as well as the behaviour of the whole system was verified using electrical simulations.

Analysis of a controversial decision process: the case of the pumped hydro storage power plant Atdorf in Germany

Based on the report for the unit “Métodos Interactivos de Participação e Decisão A” (Interactive methods of participation and decision A), coordinated by Prof. Lia Maldonado Teles de Vasconcelos and Prof. Nuno Miguel Ribeiro Videira Costa. This unit was provided for the PhD Program in Technology Assessment in 2015/2016.

A type system for value-dependent information flow analysis

Information systems are widespread and used by anyone with computing devices as well as corporations and governments. It is often the case that security leaks are introduced during the development of an application. Reasons for these security bugs are multiple but among them one can easily identify that it is very hard to define and enforce relevant security policies in modern software. This is because modern applications often rely on container sharing and multi-tenancy where, for instance, data can be stored in the same physical space but is logically mapped into different security compartments or data structures. In turn, these security compartments, to which data is classified into in security policies, can also be dynamic and depend on runtime data. In this thesis we introduce and develop the novel notion of dependent information flow types, and focus on the problem of ensuring data confidentiality in data-centric software. Dependent information flow types fit within the standard framework of dependent type theory, but, unlike usual dependent types, crucially allow the security level of a type, rather than just the structural data type itself, to depend on runtime values. Our dependent function and dependent sum information flow types provide a direct, natural and elegant way to express and enforce fine grained security policies on programs. Namely programs that manipulate structured data types in which the security level of a structure field may depend on values dynamically stored in other fields The main contribution of this work is an efficient analysis that allows programmers to verify, during the development phase, whether programs have information leaks, that is, it verifies whether programs protect the confidentiality of the information they manipulate. As such, we also implemented a prototype typechecker that can be found at http://ctp.di.fct.unl.pt/DIFTprototype/.

Continuidade e mudança. O sistema internacional no post‐Guerra Fria

O fim da Guerra Fria é um caso inédito de mudança pacífica da estrutura internacional, em que os Estados Unidos e a União Soviética transcendem a divisão bipolar para decidir os termos da paz no quadro das instituições que definem o modelo de ordenamento multilateral, consolidando a sua legitimidade. Nesse contexto, ao contrário dos casos precedentes de reconstrução internacional no fim de uma guerra hegemónica, o novo sistema do post-Guerra Fria, caracterizado pela unipolaridade, pela regionalização e pela homogeneização, forma-se num quadro de continuidade institucional. A ordem política do post-Guerra Fria é um sistema misto em que as tensões entre a hierarquia unipolar e a anarquia multipolar, a integração global e a fragmentação regional e a homogeneidade e a heterogeneidade política, ideológica e cultural condicionam as estratégias das potências. As crises internacionais vão pôr à prova a estabilidade da nova ordem e a sua capacidade para garantir mudanças pacíficas. A primeira década do post-Guerra Fria mostra a preponderância dos Estados Unidos e a sua confiança crescente, patente nas Guerras do Golfo Pérsico e dos Balcãs, bem como na crise dos Estreitos da Formosa. A reacção aos atentados do "11 de Setembro" revela uma tentação imperial da potência unipolar, nomeadamente com a invasão do Iraque, que provoca uma crise profunda da comunidade de segurança ocidental. A vulnerabilidade do centro da ordem internacional é confirmada pela crise constitucional europeia e pela crise financeira global. Essas crises não alteram a estrutura de poder mas aceleram a erosão da ordem multilateral e criam um novo quadro de possibilidades para a evolução internacional, que inclui uma escalada dos conflitos num quadro de multipolaridade regional, uma nova polarização entre as potências democráticas conservadoras e uma coligação revisionista autoritária, bem como a restauração de um concerto entre as principais potências internacionais.