The linear variable stability Transfer Function Simulation Model (TFSM), inspired by the United States Air Force's NF-16D Variable stability In-flight Simulator Test Aircraft (VISTA) and created by Henrik Pettersson, can simulate any desired aircraft. The TFSM represents a non-linear aircraft model with its stability parameters - a collection of gain constants, time constants, damping ratios, and natural frequencies. Stability parameters for aircraft generally fall into two uncoupled modes: longitudinal and lateral-directional. Unfortunately, flight tests using the TFSM exhibited undesired lateral-directional coupling in the longitudinal responses. An S-turn maneuver, formation flight test, and an uncontrolled simulation with an initial bank angle of 60 degrees were the foundation for the investigation to pinpoint the TFSM's errors. The flight tests and subsequent analysis showed that although this model is highly versatile, it has three fundamental problems. First, the original creation of the TFSM incorrectly assumed that the time rate of change for the pitch angle (in the local-horizontal reference frame) is equal to the body-axis pitch-rate for all flight conditions. Second, the TFSM's dynamics do not contain gravity terms. Third, the TFSM cannot generate the angular rates needed in a turn. Integrating the aircraft's pitch, roll, and yaw angles with the equations of motion for aircraft fixed the first problem. Unfortunately, resolving this issue only intensified the second two problems. The results from this thesis show that the last two problems are part of the TFSM and cannot be fixed explicitly. / Master of Science

A method to obtain the exact control-to-output and input-to-output transfer functions for switched DC-to-DC pulse-width modulated power converters is applied to different combinations of operating conditions such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), and discontinuous voltage mode (DVM) and methods of control such as normal voltage mode (NVM), current programming mode (CPM), and V-squared control. The majority of these combinations have not previously had their transfer functions of interest derived to the accuracy provided by the method. The derivation of the method is covered, and the results from its application are verified by simulation. The simulation method is also justied and proposed as an improvement to the methods used by simulation engines for switched mode power supply design such as SIMPLIS.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

Thesis. 1975. M.S. cn--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 93-94. / by Hugo Scaletti Farina. / M.S.cn

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Doctor of Philosophy / This dissertation provides an overview of my research over the last five years into the spectral analysis involved in human sound localization. The work involved conducting psychophysical tests of human auditory localization performance and then applying analytical techniques to analyze and explain the data. It is a fundamental thesis of this work that human auditory localization response directions are primarily driven by the auditory localization cues associated with the acoustic filtering properties of the external auditory periphery, i.e., the head, torso, shoulder, neck, and external ears. This work can be considered as composed of three parts. In the first part of this work, I compared the auditory localization performance of a human subject and a time-delay neural network model under three sound conditions: broadband, high-pass, and low-pass. A “black-box” modeling paradigm was applied. The modeling results indicated that training the network to localize sounds of varying center-frequency and bandwidth could degrade localization performance results in a manner demonstrating some similarity to human auditory localization performance. As the data collected during the network modeling showed that humans demonstrate striking localization errors when tested using bandlimited sound stimuli, the second part of this work focused on human sound localization of bandpass filtered noise stimuli. Localization data was collected from 5 subjects and for 7 sound conditions: 300 Hz to 5 kHz, 300 Hz to 7 kHz, 300 Hz to 10 kHz, 300 Hz to 14 kHz, 3 to 8 kHz, 4 to 9 kHz, and 7 to 14 kHz. The localization results were analyzed using the method of cue similarity indices developed by Middlebrooks (1992). The data indicated that the energy level in relatively wide frequency bands could be driving the localization response directions, just as in Butler’s covert peak area model (see Butler and Musicant, 1993). The question was then raised as to whether the energy levels in the various frequency bands, as described above, are most likely analyzed by the human auditory localization system on a monaural or an interaural basis. In the third part of this work, an experiment was conducted using virtual auditory space sound stimuli in which the monaural spectral cues for auditory localization were disrupted, but the interaural spectral difference cue was preserved. The results from this work showed that the human auditory localization system relies primarily on a monaural analysis of spectral shape information for its discrimination of directions on the cone of confusion. The work described in the three parts lead to the suggestion that a spectral contrast model based on overlapping frequency bands of varying bandwidth and perhaps multiple frequency scales can provide a reasonable algorithm for explaining much of the current psychophysical and neurophysiological data related to human auditory localization.

<p>In quantitative palaeoecology modern species-environmental relationships can be statistically modelled, and recent development has made the calibration models more statistically robust. These models are used to transform fossil assemblages to quantitative estimates of past environmental conditions. The aim of this thesis is to infer Holocene temperatures from fossil pollen data sampled from lakes in central and southern Sweden. This reconstruction is done by using a north-European pollen-climate calibration model, which was extended with 37 modern pollen samples from the southern deciduous vegetation zone in Sweden within this project. A statistical method is used for deriving the pollen-climate calibration model, weighted averaging partial least square (WA-PLS) method. The long term trends in pollen inferred temperatures from this study reflect low, but rapidly rising temperatures in the early-Holocene, a trend that was temporarily interrupted by a cool period about 8500 cal yr BP, but continued after 8000 cal yr BP. A Holocene thermal maximum (HTM) with temperatures roughly 2°C higher than at present was recorded about 7000 cal yr BP and by 4000 cal yr BP pollen inferred temperatures starts to decline. In order to create a more comprehensive picture of past climate patterns in the investigated area inferred temperatures from this study are compared with independent palaeorecords, a stable oxygen isotope record for moisture variability (paper I) and chironomids for summer temperature (paper II). Taken all together, these records reflect a coherent Holocene climate pattern which also is supported by several studies from Scandinavia and the north Atlantic region. Pollen inferred temperatures and the moisture record are indicating markedly dry, continental climate conditions in southern Sweden during the HTM possibly as a result of reorganisations in regional atmosphere circulations. The local observations in this study of regional climate events, such as the cold period at about 8200 cal yr BP and the dry period at about 7000 to 4000 cal yr BP are of particular interest because they suggest that vegetation in the study region has responded sensitively both to long-term climatic trends and more transient climate events.</p>

In this paper, the problem of dual actuation in the atomic force microscope (AFM) is analyzed. The use of two actuators to balance the trade-off between bandwidth, range, and precision has been recently extended to nano-positioning systems. Despite existing demands, this concept undergoes fundamental limitations towards its extension to AFMs. This is attributed to the non-conventional requirement imposed on the control signal response, as it used to create the image of the characterized surface. / Singapore-MIT Alliance (SMA)