Determinants and effects of electoral party coalitions: The case of Brazil

Since the 1985 return to democracy, Brazilian politicians have resorted to vote-pooling arrangements to elect representatives. A puzzle thus presents itself: What drives parties to join these electoral cartels? The dissertation unraveled the incentives party elites have to participate in coalitions under a presidencialist system of government. I also investigated the effect of electoral coalitions on congressional representation. I applied a model of binary outcomes and relied on standard deviations to assess the ideological homogeneity/heterogeneity of electoral coalitions. I also calculated the Index of Disproportionality to measure the gaps between the proportion of votes and seats received by all parties in Brazil with and without electoral coalitions. Finally, I assessed the effects of the electoral formula on proportionality. An unexpected exogenous factor resulted crucial in explaining proportional electoral coalition building: The district's majoritarian election for governor. In each district, political actors often synchronize coalition partners to maximize winning results while minimizing electoral efforts.

Optimizing storage and memory systems for energy and performance

Electrical energy is an essential resource for the modern world. Unfortunately, its price has almost doubled in the last decade. Furthermore, energy production is also currently one of the primary sources of pollution. These concerns are becoming more important in data-centers. As more computational power is required to serve hundreds of millions of users, bigger data-centers are becoming necessary. This results in higher electrical energy consumption. Of all the energy used in data-centers, including power distribution units, lights, and cooling, computer hardware consumes as much as 80%. Consequently, there is opportunity to make data-centers more energy efficient by designing systems with lower energy footprint. Consuming less energy is critical not only in data-centers. It is also important in mobile devices where battery-based energy is a scarce resource. Reducing the energy consumption of these devices will allow them to last longer and re-charge less frequently. Saving energy in computer systems is a challenging problem. Improving a system's energy efficiency usually comes at the cost of compromises in other areas such as performance or reliability. In the case of secondary storage, for example, spinning-down the disks to save energy can incur high latencies if they are accessed while in this state. The challenge is to be able to increase the energy efficiency while keeping the system as reliable and responsive as before. This thesis tackles the problem of improving energy efficiency in existing systems while reducing the impact on performance. First, we propose a new technique to achieve fine grained energy proportionality in multi-disk systems; Second, we design and implement an energy-efficient cache system using flash memory that increases disk idleness to save energy; Finally, we identify and explore solutions for the page fetch-before-update problem in caching systems that can: (a) control better I/O traffic to secondary storage and (b) provide critical performance improvement for energy efficient systems.