This work focuses on the problem of planning solar array operations on the International Space Station. The goal is to find a viable orientation for ten joints which attach panels to the station. These orientations and modes must satisfy various constraints and the final schedule should also take into account certain preferences. This is a task suitable for automated planning and scheduling, but new technologies are gaining very slowly in the field of the human spaceflights. In this work we will analyze the current solution of this problem and then we will propose a new algorithm that will exploit techniques of automated planning and scheduling. In the contrast with the original greedy algorithm, the suggested algorithm initially finds any solution and then tries to improve it by optimazing partial objective functions. Due to the size of the search space, the search attempts are limited by the time limit. Powered by TCPDF (www.tcpdf.org)

The stimuli response of a polymer – metal bilayer architecture was investigated. This solvent activated system showed a dynamic response when exposed to a particular solvent. Polymer wires were fabricated using a glass capillary array (GCA) as a template. The synthesized wires were then sputtered with silver and exposed to dichloromethane (DCM). The solvent activated response results in a number of physical distortions of which the circular deformation was the most predominant. The thicknesses of the metal coating and the direction of the solvent front were studied in an effort to determine their relationship to the observed wired deformations.

Thesis advisor: Michael J. Naughton / Thesis advisor: Michael J. Burns / Recent progress in the study of the brain has been greatly facilitated by the development of new measurement tools capable of minimally-invasive, robust coupling to neuronal assemblies. Two prominent examples are the microelectrode array, which enables electrical signals from large numbers of neurons to be detected and spatiotemporally correlated, and optogenetics, which enables the electrical activity of cells to be controlled with light. In the former case, high spatial density is desirable but, as electrode arrays evolve toward higher density and thus smaller pitch, electrical crosstalk increases. In the latter, finer control over light input is desirable, to enable improved studies of neuroelectronic pathways emanating from specific cell stimulation. Herein, we introduce a coaxial electrode architecture that is uniquely suited to address these issues, as it can simultaneously be utilized as an optical waveguide and a shielded electrode in dense arrays. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Thesis advisor: Michael Graf / Bismuth is an interesting element to study because the low effective mass of its charge carriers makes the material sensitive to quantum confinement effects. When bismuth is reduced to the nanoscale two interesting phenomena may occur: it may transition from a semimetal to a semiconductor, or charge carriers in special surface states may begin to dominate the behavior of the material. Arrays of bismuth nanowires of various diameters were studied to investigate these possibilities. The magnetoresistance of the arrays was measured and the period of Shubnikov-de Haas oscillations suggested an increase in the effective mass and density of the material’s charge carriers for small nanowire diameters. These increases suggested that electrons were present in surface states and strongly influenced the material’s behavior when its dimensions were sufficiently reduced. The magnetization of the nanowire arrays was also measured and the lack of de Haas-van Alphen oscillations for certain diameter nanowires suggested that electrons were not present in surface states and that instead the material was transitioning from a semimetal to a semiconductor. Heat capacity measurements were planned to reconcile the two experiments. My detailed calculations demonstrated that heat capacity measurements were feasible to determine the presence, or absence, of surface charge carriers. Because the electronic contribution to the material’s heat capacity is small a calorimeter platform was constructed with ultra-low heat capacity components. / Thesis (BS) — Boston College, 2009. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Physics.

The use of biosensors and microfluidics devices is often limited by constraints in terms of volumetric throughput due to the small dimensions of devices in microfluidics and of expensive and complicated sample preparation steps necessary to ensure the operation of biosensing platforms. This can be due to high initial sample volume with low concentration analytes or complex media matrices from which analytes are extracted. While working to analyse Cryptosporidium presence in drinking water a novel technique was developed. The huge advantages from using a label-free, buffer-free hydrodynamic mechanism in terms of cost, coupled with the ease of simply scaling a single design to match any target size and the ability manufacture these quickly and easily using cheap and readily available robust materials (i.e. acrylic sheet) may allow a revolution in the scope of microfluidics applications. Using a cascaded array of hydrodynamic focusing devices uniquely designed for parallelised operation from a single pump or pressure source, the array can be tailored to meet the specific requirements of many applications, in particular high volume and low concentration target analyte enrichment from complex media.

In antenna array processing it is generally required to enhance the reception or detection of a signal from a particular direction while suppressing noise and interference signals from other directions. An optimisation problem often posed to achieve this result is to minimise the array processor mean output power (or variance) subject to a fixed response in the array look direction. The look direction requirement can be met by imposing a set of linear constraints on the processor weights to yield what is known as the Linearly Constrained Minimum Variance (LCMV) processor. It has been found, however, that LCMV processors are susceptible to errors in the assumed direction of arrival of the desired signal. To achieve robustness against directional mismatch, additional constraints known as derivative constraints can be introduced. These constraints force the first and second order spatial derivatives of the array power response in the look direction to zero. However, constraints corresponding to necessary and sufficient (NS) conditions for these spatial derivatives to be zero are in general quadratic, and the resulting weight vector solution space is non-convex. One approach to this complex problem has been to consider conditions which are only sufficient for the spatial derivatives to be zero. Whilst this results in linear constraints, it exhibits certain anomalous behaviour, for example, dependence on the choice of array phase centre.Recent work in the area of derivative constraints has resulted in a method for efficiently solving the non-convex output power minimisation problem with quadratic derivative constraints. The optimisation problem addressed assumes that the input signal statistics and hence the input signal autocorrelation matrix R are known. In practice, R must be estimated from the receiver data.The main contribution of this thesis is the derivation of a ++ / new adaptive algorithm which implements an adaptive array processor with look direction plus 1st and 2nd order NS derivative constraints. The new algorithm is derived from the well-known Recursive Least Squares (RLS) technique but allows linear and quadratic constraints to be incorporated within the recursive framework. The algorithm offers the high performance characteristics associated with RLS methods, namely, fast convergence and high steady-state accuracy. The work encompasses a study of the characteristics of the algorithm in terms of numerical robustness, convergence properties, tracking and computational complexity.The study of the numerical properties of the algorithm has led to the second important contribution of this thesis: the identification of a parameter which is central to the numerical stability of the algorithm in a practical fixed precision environment. We show that this parameter is bounded during stable operation and can therefore be used to detect the onset of numerical instability within the algorithm. In addition, we show how existing techniques can be used to significantly improve the numerical robustness of the algorithm.Another important contribution of the thesis stems from an investigation into the multimodal nature of the quadratic, equality constrained optimisation problem resulting from the use of second order NS derivative constraints. In particular, we show that for a linear antenna array operating under certain conditions, the complex multimodal optimisation problem can be greatly simplified. This has important implications in both optimum and adaptive array signal processing.

The work described in this thesis tested the feasibility of using a towed array of hydrophones to: 1. localise sources of underwater acoustic noise radiated by the towvessel, 2. determine the absolute amplitudes of these sources, and 3. determine the resulting far-field acoustic signature of the tow-vessel. The concept was for the towvessel to carry out a U-turn manoeuvre so as to bring the acoustic section of the array into a location suitable for beamforming along the length of the tow-vessel. All three of the above were shown to be feasible using both simulated and field data, although no independent field measurements were available to fully evaluate the accuracy of the far-field acoustic signature determinations. A computer program was written to simulate the acoustic signals received by moving hydrophones. This program had the ability to model a variety of acoustic sources and to deal with realistic acoustic propagation conditions, including shallow water propagation with significant bottom interactions. The latter was accomplished using both ray and wave methods and it was found that, for simple fluid half-space seabeds, a modified ray method gave results that were virtually identical to those obtained with a full wave method, even at very low frequencies, and with a substantial saving in execution time. A field experiment was carried out during which a tug towing a 60-hydrophone array carried out a series of U-turn manoeuvres. The signals received by the array included noise radiated by the tow-vessel, signals from acoustic tracking beacons mounted on the tow-vessel, and transient signals generated by imploding sources deployed from a second vessel. / Algorithms were developed to obtain snapshots of the vertical plane and horizontal plane shapes of the array from the transient data and to use range data derived from the tracking beacon signals to track the hydrophones in the horizontal plane. The latter was complicated by a high proportion of dropouts and outliers in the range data caused by the directionality of the hydrophones at the high frequencies emitted by the beacons. Despite this, excellent tracking performance was obtained. Matched field inversion was used to determine the vertical plane array shapes at times when no transient signals were available, and to provide information about the geoacoustic properties of the seabed. There was very good agreement between the inversion results and array shapes determined using transient signals. During trial manoeuvres the array was moving rapidly relative to the vessel and changing shape. A number of different array-processing algorithms were developed to provide source localisation and amplitude estimates in this situation: a timedomain beamformer; two frequency-domain, data independent beamformers; an adaptive frequency-domain beamformer; and an array processor based on a regularised least-squares inversion. The relative performance of each of these algorithms was assessed using simulated and field data. Data from three different manoeuvres were processed and in each case a calibrated source was localised to within 1 m of its known position at the source's fundamental frequency of 112 Hz. / Localisation was also successful in most instances at 336 Hz, 560 Hz and 784 Hz, although with somewhat reduced accuracy due to lower signal to noise ratios. Localisation results for vessel noise sources were also consistent with the positions of the corresponding items of machinery. The estimated levels of the calibrated source obtained during the three manoeuvres were all within 4.1 dB of the calibrated value, and varied by only 1.3 dB between manoeuvres. Results at the higher frequencies had larger errors, with a maximum variation of 3.8 dB between serials, and a maximum deviation from the calibrated value of 6.8 dB. An algorithm was also developed to predict the far-field signature of the tow-vessel from the measured data and results were produced. This algorithm performed well with simulated data but no independent measurements were available to compare with the field results.

This thesis examines the problem of reducing reconfiguration time of an island-style FPGA at its configuration memory level. The approach followed is to examine configuration encoding techniques in order to reduce the size of the bitstream that must be loaded onto the device to perform a reconfiguration. A detailed analysis of a set of benchmark circuits on various island-style FPGAs shows that a typical circuit randomly changes a small number of bits in the {\it null} or default configuration state of the device. This feature is exploited by developing efficient encoding schemes for configuration data. For a wide set of benchmark circuits on various FPGAs, it is shown that the proposed methods outperform all previous configuration compression methods and, depending upon the relative size of the circuit to the device, compress within 5\% of the fundamental information theoretic limit. Moreover, it is shown that the corresponding decoders are simple to implement in hardware and scale well with device size and available configuration bandwidth. It is not unreasonable to expect that with little modification to existing FPGA configuration memory systems and acceptable increase in configuration power a 10-fold improvement in configuration delay could be achieved. The main contribution of this thesis is that it defines the limit of configuration compression for the FPGAs under consideration and develops practical methods of overcoming this reconfiguration bottleneck. The functional density of reconfigurable devices could thereby be enhanced and the range of potential applications reasonably expanded.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 216-221).

<p>Future radars require more flexible and faster radar signal processing chain than commercial radars of today. This means that the demands on the processors in a radar signal system, and the desire to be able to compute larger amount of data in lesser time, is constantly increasing. This thesis focuses on commercial micro-processors of today that can be used for Active Electronically Scanned Array Antenna (AESA) based radar, their physical size, power consumption and performance must to be taken into consideration. The evaluation is based on theoretical comparisons among some of the latest processors provided by PACT, PicoChip, Intrinsity, Clearspeed and IBM. The project also includes a benchmark made on PowerPC G5 from IBM, which shows the calculation time for different Fast Fourier Transforms (FFTs). The benchmark on the PowerPC G5 shows that it is up to 5 times faster than its predecessor PowerPC G4 when it comes to calculate FFTs, but it only consumes twice the power. This is due to the fact that PowerPC G5 has a double word length and almost twice the frequency. Even if this seems as a good result, all the PowerPC´s that are needed to reach the performance for an AESA radar chain would consume too much power. The thesis ends up with a discussion about the traditional architectures and the new multi-core architectures. The future belongs with almost certainty to some kind of multicore processor concept, because of its higher performance per watt. But the traditional single core processor is probably the best choice for more moderate-performance systems of today, if you as developer looking for a traditional way of programing processors.</p>