Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by André Antoine Merab. / M.S.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Vita. / Includes bibliographical references. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by John A. Cartelli. / M.S.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

<p>Connectionist models have been criticized for not being able to form compositional representations of recursive data structures such as trees and lists, a matter that has been addressed by models as Elman networks, RAAM and B-RAAM. These architectures seem to have common features with the human short-term memory regarding recall. Both show a strong recency effect; however, the human memory also exhibits a primacy effect due to rehearsal. The problem is that the connectionist models do not have the primacy aspect, which complicates the learning of long-term dependencies. A long-term dependency is when items presented early should affect the behaviour of the model. Learning long-term dependencies is a problem that is hard to address within these architectures.</p><p>Delay-lines might be used as a mechanism for implementing rehearsal within connectionist models. However, it has not been clarified how the use of delay-lines affects the recency and the primacy aspect. In this thesis, delay-lines are introduced in B-RAAM. This study investigates how the primacy and the recency aspect are affected by the use of delay-lines, aiming to improve the ability to identify long-term dependencies. The results show that by using delay-lines, B-RAAM has both primacy and recency.</p>

Connectionist models have been criticized for not being able to form compositional representations of recursive data structures such as trees and lists, a matter that has been addressed by models as Elman networks, RAAM and B-RAAM. These architectures seem to have common features with the human short-term memory regarding recall. Both show a strong recency effect; however, the human memory also exhibits a primacy effect due to rehearsal. The problem is that the connectionist models do not have the primacy aspect, which complicates the learning of long-term dependencies. A long-term dependency is when items presented early should affect the behaviour of the model. Learning long-term dependencies is a problem that is hard to address within these architectures. Delay-lines might be used as a mechanism for implementing rehearsal within connectionist models. However, it has not been clarified how the use of delay-lines affects the recency and the primacy aspect. In this thesis, delay-lines are introduced in B-RAAM. This study investigates how the primacy and the recency aspect are affected by the use of delay-lines, aiming to improve the ability to identify long-term dependencies. The results show that by using delay-lines, B-RAAM has both primacy and recency.

Thesis: M.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1976 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

There has been a tremendous growth in the computer, television and RADAR fields. As a result, demands on the components that give time control over pulse information have led to the development of a great variety of delay lines. Delay lines are used in the systems that relate electrical information to time like computers, television, telemetering systems, guiding missiles, navigating systems, identifying coders and decoders, radar systems and video tape recorders are typical systems that use delay lines. Delay lines are also used in electronic objects for making decision point, in sound reinforcements. In a delay network, for a given bandwidth, the amount of delay increases as the order increases. Therefore we propose an idea of optimizing the poles of the filter in order to get more delay over a given order and bandwidth.

Optical filters encompass a vast array of devices and structures for a wide variety of applications. Generally speaking, an optical filter is some structure that applies a designed amplitude and phase transform to an incident signal. Different classes of filters have vastly divergent characteristics, and one of the challenges in the optical design process is identifying the ideal filter for a given application and optimizing it to obtain a specific response. In particular, it is highly advantageous to obtain a filter that can be seamlessly integrated into an overall device package without requiring exotic fabrication steps, extremely sensitive alignments, or complicated conversions between optical and electrical signals. This dissertation explores three classes of nano-scale optical filters in an effort to obtain different types of dispersive response functions. First, dispersive waveguides are designed using a sub-wavelength periodic structure to transmit a single TE propagating mode with very high second order dispersion. Next, an innovative approach for decoupling waveguide trajectories from Bragg gratings is outlined and used to obtain a uniform second-order dispersion response while minimizing fabrication limitations. Finally, high Q-factor microcavities are coupled into axisymmetric pillar structures that offer extremely high group delay over very narrow transmission bandwidths. While these three novel filters are quite diverse in their operation and target applications, they offer extremely compact structures given the magnitude of the dispersion or group delay they introduce to an incident signal. They are also designed and structured as to be formed on an optical wafer scale using standard integrated circuit fabrication techniques. A number of frequency-domain numerical simulation methods are developed to fully characterize and model each of the different filters. The complete filter response, which includes the dispersion and delay characteristics and optical coupling, is used to evaluate each filter design concept. However, due to the complex nature of the structure geometries and electromagnetic interactions, an iterative optimization approach is required to improve the structure designs and obtain a suitable response. To this end, a Particle Swarm Optimization algorithm is developed and applied to the simulated filter responses to generate optimal filter designs.

The field of superconductivity has recently begun to grow in an exponential fashion. This thesis has briefly described a history of superconductivity discoveries, provided the brief literature review about the superconductors. The superconductor material realization and characterization are provided. The delay line design method is presented and various printed delay lines are constructed. The experimental results are presented and discussed. / Master of Science