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This project compares four different hedging techniques using spot and futures exchange rates of the British Pound. Specifically, the OLS regression model, the vector autoregressive model (VAR), the vector error correction model (VECM) and the Multivariate GARCH with error correction model are applied. Hedging effectiveness is measured in terms of minimizing variance of hedged portfolios. The VAR model and the VECM offer the same performance, which is higher than that of the OLS model. Although the multivariate GARCH with error correction model is the only one being able to capture the time varying nature of the hedge ratio, the hedging performances of four str ategies do not differ very much, either in-sample or out-of-sample. Therefore, although complex models are able to capture more figures of the data set, there is no evidence that they will give significant better hedging performance.

In recent years, aircraft manufacturers have been making progress in the design of more efficient aircrafts to reduce the environmental footprint. To attain this target, aircrafts manufactures work on the replacement of the hydraulic and bleed systems for electrical systems leading to a “More Electrical Aircraft”. However, the expected mass gain is a challenge, as previous technologies have been developed and optimized for decades. The new electrical solutions need to be look into detail to be competitive with previous technologies. All degrees of freedom must be considered, that is, new technologies and architectures. In particular, an HVDC network that reduces the number of rectifier stages seems a promising solution. From the HVDC network, the different three phase AC loads will be supplied by a series of power generic inverters. As the power consumption of the different loads change during the flight mission, the same inverter is used to supply different loads. The connection between the inverters and the loads is managed by a matrix of contactors. The proposed solution also considers redundant configurations, thus increasing system robustness. The design of the innovative system is presented in this document. That is, determining the optimal trade-off between the number of power inverters and the nominal power of each generic inverter that will also impact the size of the matrix of contactors. However, to assess the combinatory problem, the mass of the different components as a function of the nominal power needs to be calculated. A design environment is therefore created to perform automatic and optimized design of power converters. The different components are described using a “direct modelling” approach and coded using “object-oriented” programming. The components are validated experimentally or by numerical simulations. The different models are coupled to an optimization environment and to a frequency solver allowing a fast calculation of the steady-state waveforms. The optimization environment performs the precise design of the different parts of the power inverter: heatsink, power module, DC filter and coupling inductor. The power inverter is designed for different values of nominal power and switching frequency. The optimization assesses as well the usage of different technologies. Finally, the results are used to determine the optimal trade-off between the number of inverters and the nominal power of each inverter using a heuristic algorithm.

A low-cost thermal pressure sensor based on short-distance thermal conduction and used in atmospheric pressure range has been explored. This simple device consists of a heater made of a polysilicon resistor, a heat sink made by the silicon substrate and a tiny air gap between them. With innovative ideas and simple processes, the gap can be made in the order of nanometers inexpensively, which significantly increases the measurement range of the sensor. Devices capable of measuring 700kPa (7atm) or more have been fabricated with a 3-mask, 3pm and CMOS compatible process. The device can be made as small as 50x50pm2, less than the size of a standard bonding pad. The simple process and low cost associated with these devices could make commercial adaptation promising.

The exchange stiffness, Aex, is one of the key parameters controlling magnetization reversal in magnetic materials but is very difficult to measure, especially in thin films. We developed a new technique for measuring the exchange stiffness of a magnetic material based on the formation of a spin spiral within two antiferromagnetically coupled ferromagnetic films [1]. Using this method, I was able to measure the exchange stiffness of thin film Co alloyed with Cr, Fe, Ni, Pd, Pt and Ru. The results of this work showed that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. These measured trends have been understood by combining measurements of element specific magnetic moments obtained using X-ray magnetic circular dichroism (XMCD) and material specific modeling based on density functional theory (DFT) within the local density approximation (LDA). The experimental results also hint at significant reduction of the exchange stiffness at the interface that can account for the difference between our results and those obtained on bulk materials.

In light of the existence of an informal sector in most developing countries, economists are beginning to reconsider the integrated tax reform consisting of a reduction in tari®s with an increase in VAT that has been advocated by the IMF in recent years. This paper explores the welfare change of such a reform in an economy in which the size of the informal sector is endogenously determined. Assuming that products are nontraded, the levy of VAT distorts the aggregate output; allowing the size of the informal sector to be determined endogenously worsens the situation. This leads to a conclusion which tends to favor an integrated tax reform toward tari®s under some plausible conditions. This result may help to explain the slow adoption of VAT in many developing countries.

As optical tweezers become widely used in biophysics, calibration becomes essential to quantitatively characterize the dynamics of a system probed by this technique. In this thesis, I apply three methods for calibrating optical tweezers: a direct estimate from thermal motion of a trapped particle using the equipartition theorem, a more advanced approach that analyzes its power spectrum, and a combination of power spectrum analysis and the bead’s response under an external driving force. Motivated by recent attempts to use parametric resonance for calibration, I also examine the effects of modulating laser power on the motion of the trapped particle, predicting and finding experimentally an increase in the particle’s position variance at low modulation frequencies without evidence for resonant effects in the extremely overdamped motion of the trapped particle. I conclude by discussing future considerations such as the treatment of hydrodynamics and the effect of an anharmonic trap potential.