Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Hasler, Paul; Committee Member: Anderson, David; Committee Member: Ghovanloo, Maysam. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2003. / Includes bibliographical references (p. 229-232).

Thesis--Auburn University, 2010. / Abstract. Includes bibliographic references (p.162-167).

Numerical modeling techniques commonly used to compute the response of soil and rock media under earthquake shaking are evaluated by analyzing the observations provided by instrumented borehole arrays. The NIED Kik-Net database in Japan is selected as the main source of borehole array data for this study. The stiffness of the site and the availability of high intensity motions are the primary factors considered towards the selection of appropriate Kik-Net borehole arrays for investigation. Overall, 13 instrumented vertical arrays are investigated using over 750 recorded ground motions characterized by low (less than 0.05 g) to high (greater than 0.3 g) recorded peak ground accelerations at the downhole sensor. Based on data from the selected borehole arrays, site response predictions using 1-D linear elastic (LE) analysis, equivalent linear (EQL) analysis, equivalent linear analysis with frequency-dependent soil properties (EQL-FD), and fully nonlinear analysis (NL) are compared with the borehole observations. Initially, the low intensity motions are used to evaluate common assumptions regarding 1-D site response analysis. First, we identify the borehole wavefield best simulating the actual boundary condition at depth by comparing the theoretical linear-elastic (LE) and observed responses. Then, we identify the best-fit small-strain damping profiles that can incorporate the additional in-situ attenuation mechanisms. Finally, we assess the validity of the one-dimensional modeling assumption. Our analyses indicate that the appropriate boundary condition for analysis of a borehole array depends on the depth of the borehole sensor and that, for most of the considered vertical arrays, the one-dimensional assumption reasonably simulates the actual wave propagation pattern. In the second part of this study, we evaluate the accuracy of the EQL, EQL-FD and NL site response methods by quantifying the misfit (i.e., residual) between the simulations and observations at different levels of shaking. The evaluation of the performance of the theoretical models is made both on a site-by-site basis and in an aggregated manner. Thereafter, the variability in the predicted response from the three site response methods is assessed. Comparisons with the observed responses indicate that the misfit of simulations can be significant at short periods and large strains. Moreover, all models seem to be characterized by the same level of variability irrespectively of the level of shaking. Finally, several procedures that can be used to improve the accuracy of the one-dimensional EQL, EQL-FD and NL site response analyses, are investigated. First, an attempt to take into account the shear strength of the soil materials at large shear strains is made. Additionally, several modifications to the EQL-FD approach are proposed. The proposed modifications are evaluated against recordings from the borehole arrays. Our analyses indicate that the accuracy of the theoretical models can be, partly, increased by incorporating the proposed modifications. / text

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Η παρούσα διπλωματική εργασία αποσκοπεί στην δημιουργία ενός σύγχρονου και ευέλικτου προγράμματος σε περιβάλλον Matlab, το οποίο θα επιτυγχάνει την ορθή και λεπτομερή προσομοίωση της λειτουργίας των συστοιχιών ηχείων, μέσω της αναπαράστασης της στάθμης ηχητικής πίεσης (SPL) και των διαγραμμάτων κατευθυντικότητας, και το οποίο θα είναι εύκολο στη χρήση και φιλικό προς τον χρήστη μέσω ενός γραφικού περιβάλλοντος το οποίο θα δημιουργηθεί επίσης στο Matlab. Στην εργασία παρούσιαζονται τόσο τα στοιχεία που αποτελούν και συνθέτουν μια συστοιχία ηχείων όσο και οι μετάβλητές που επηρεάζουν την απόδοση λειτουργίας της. Παρουσιάζεται βήμα βήμα η δημιουργία και η εξέλιξη του απαιτούμενου κώδικα καθώς και επεξηγήσεις για την λειτουργία και τον τρόπο χρήσης του. Μέσω πολύπλοκων εξισώσεων γίνεται δυνατή η πλήρης και ακριβής προσομοίωση των συστοιχιών και επακόλουθα η εξαγωγή χρήσιμων συμπερασμάτων όσον αφορά τον τρόπο λειτουργίας τους, τις μεταβλήτές αλλά και τον τρόπο που αυτές επηρεάζουν την στάθμη ηχητικής πίεσης (SPL) των συστοιχιών καθώς και για τον τρόπο βελτιστοποίησης της απόδοσης μιας συστοιχίας. Η ενσωμάτωση του εν λόγω κώδικα σε ένα χρήσιμο και εύχρηστο γραφικό περιβάλλον, κάνει το εν λόγω πρόγραμμα ιδανικό για την μελέτη της συμπεριφοράς των συστοιχιών ηχείων κάτω απο οποιεσδήποτε συνθήκες. / This project presents a modern and flexible program which was created in a Matlab environment and which simulates in great detail the function of loudspeaker arrays through the representation of the Sound Pressure Level (SPL) and the Directivity Functions of all kind of loudspeaker arrays. This program is extremely user friendly since it has been embedded in a Graphic User interface, which was also created in a Matlab environment. In the project are presented the elements of which a loudspeaker array is comprised off and the different variables that affect its performance. There is a step by step presentation of the creation process and the evolution process of the Matlab code as well as instructions for the way of use of the final program. Through complex equations, it is possible to fully simulate the function of loudspeaker arrays with great detail and thus to extract very useful conclusions about their function, and the way that various variables affect their Sound Pressure Level in order to optimize their performance. The embendment of this program in an easy to handle graphic user interface, makes it ideal for the study and research of the behavior of loudspeaker arrays under any circumstances.

FPGA clock frequencies are slow enough that only a fraction of the interconnect’s bandwidth is used. By exploiting this bandwidth, the transfer of large amounts of data can be greatly accelerated. Alternatively, it may also be possible to save area on fixed-bandwidth links by using on-chip serial signaling. For datapath-intensive designs which operate on words instead of bits, this can reduce wiring congestion as well. This thesis proposes relatively simple circuit-level modifications to FPGA interconnect to enable high-bandwidth communication. High-level area estimates indicate a potential interconnect area savings of 10 to 60% when serial links are used. Two interconnect pipelining techniques, wave pipelining and surfing, are adapted to FPGAs and compared against each other and against regular FPGA interconnect in terms of throughput, reliability, area, power, and latency. Source-synchronous signaling is used to achieve high data rates with simple receiver design. Statistical models for high-frequency power supply noise are developed and used to estimate the probability of error of wave pipelined and surfing links as a function of link length and operating speed. Surfing is generally found to be more reliable and less sensitive to noise than wave pipelining. Simulation results in a 65nm process demonstrate a throughput of 3Gbps per wire across a 50-stage, 25mm link.

ZnO nanowire arrays (NWAs) and Al-doped ZnO (AZO) cathodes were applied in hybrid organic / inorganic solar cells for lower-cost solar energy. Parameters for the electrodeposition of ZnO NWAs and the fabrication of NWA-free baseline devices were systematically optimized using ITO as the cathodes. High efficiencies of up to 5.4% were achieved. Incorporation of the ZnO NWAs into the baseline devices significantly reduced their efficiencies due to possible shorting in the active layer. Devices fabricated using AZO cathodes were characterized. The AZO-based devices achieved efficiencies of up to ~4.8%, showing promising results for the application of AZO as an ITO alternative. Formation of numerous large nanoplatelets was observed during the electrodeposition of ZnO NWAs on AZO cathodes. The NWAs grown on AZO cathodes were also non-uniform. Future studies were proposed to address the issues with incorporation of ZnO NWAs in hybrid solar cells and their combination with AZO cathodes.

ZnO nanowire arrays (NWAs) and Al-doped ZnO (AZO) cathodes were applied in hybrid organic / inorganic solar cells for lower-cost solar energy. Parameters for the electrodeposition of ZnO NWAs and the fabrication of NWA-free baseline devices were systematically optimized using ITO as the cathodes. High efficiencies of up to 5.4% were achieved. Incorporation of the ZnO NWAs into the baseline devices significantly reduced their efficiencies due to possible shorting in the active layer. Devices fabricated using AZO cathodes were characterized. The AZO-based devices achieved efficiencies of up to ~4.8%, showing promising results for the application of AZO as an ITO alternative. Formation of numerous large nanoplatelets was observed during the electrodeposition of ZnO NWAs on AZO cathodes. The NWAs grown on AZO cathodes were also non-uniform. Future studies were proposed to address the issues with incorporation of ZnO NWAs in hybrid solar cells and their combination with AZO cathodes.

Collaborative beamforming is a powerful technique to increase communication energy efficiency and range in an energy-constrained network. To achieve high performance, collaborative beamforming requires accurate knowledge of channel state information (CSI) at the transmitters (collaborative nodes). In practice, however, such exact knowledge of CSI is not available. A robust transmitter design based on partial CSI is required to mitigate the effects of CSI mismatches. / This thesis focuses on the design and evaluation of a beamforming scheme that is robust to CSI mismatches for collaborative multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless systems. Using a max-min robust design approach, the robust beamformer is designed to maximize the minimum (worst-case) received signal-to-noise ratio (SNR) within a predefined uncertainty region at each OFDM subcarrier. In addition, several subcarrier power allocation strategies are investigated to further improve the robustness of collaborative systems. Numerical simulation results show that the robust beamformer offers improved performance over the nonrobust beamformers and the use of power allocation strategies among subcarriers further improves the system performance.