Departmental Honors Advisor

In this thesis we argue that content distribution in the face of censorship is an appropriate and feasible application of active networking. In the face of a determined and powerful adversary, every fixed protocol can become known and subsequently monitored, blocked, or its member nodes identified and attacked. Rapid and diverse protocol change is key to allowing information to continue to flow. Typically, decentralized protocol evolution is also an important aspect in providing censor-resistance for publishing networks. These goals can be achieved with the help of active networking techniques, by allowing new protocol implementations, in the form of mobile code, to spread throughout the network. A programmable overlay network can provide protocol change and decentralized protocol evolution. Such a system, however, will need to take steps to ensure that programmability does not present excessive security threats to the network. Runtime isolation, protocol confidence ratings, encryption, and resource control are vital in this respect. We have prototyped such a system as an extension to Freenet, a storage and retrieval system whose goals include censor resistance and anonymity for informa-tion publishers and consumers. Our prototype implements many of the mechanisms discussed in this thesis, indicating that our proposed ideas are feasible to imple-ment. i

Optical modelling and analysis of the Q and U bolometric interferometer for cosmology

Remnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines. The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane. The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results. In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner