The behavior of structures is totally different when they are exposed to fluctuating loading rather than static one which is a well known phenomenon in engineering called fatigue. When the loading is not static but dynamic, the dynamics of the structure should be taken into account since there is a high possibility to excite the resonance frequencies of the structure especially if the loading frequency has a wide bandwidth. In these cases, the structure&rsquo / s response to the loading will not be linear. Therefore, in the analysis of such situations, frequency domain fatigue analysis techniques are used which take the dynamic properties of the structure into consideration. Vibration fatigue method is also fast, functional and easy to implement. In this thesis, vibration fatigue theory is examined. Throughout the research conducted for this study, the ultimate aim is to find solutions to problems arising from test application for the loadings with nonzero mean value bringing a new perspective to mean stress correction techniques. A new method is developed to generate a modified input loading history with a zero mean value which leads in fatigue damage approximately equivalent to damage induced by input loading with a nonzero mean value. A mathematical procedure is proposed to implement mean stress correction to the output stress power spectral density data and a modified input loading power spectral density data is obtained. Furthermore, this method is improved for multiaxial loading applications. A loading history power spectral density set with zero mean but modified alternating stress, which leads in fatigue damage approximately equivalent to the damage caused by the unprocessed loading set with nonzero mean, is extracted taking all stress components into account using full matrixes. The proposed techniques&rsquo / efficiency is discussed throughout several case studies and fatigue tests.

During the last decade, the transit method has evolved to one of the most promising techniques in the search for extrasolar planets and the quest to find other earth-like worlds. In theory, the transit method is straight forward being based on the detection of an apparent dimming of the host star’s light due to an orbiting planet traversing in front of the observer. However, in practice, the detection of such light curve dips and their confident ascription to a planetary transit is heavily burdened by the presence of different sources of noise, the most prominent of which is probably the so called intrinsic stellar variability. Filtering out potential transit signals from background noise requires a well adjusted high-pass filter. In order to optimize such a filter, i.e. to achieve best separation between signal and noise, one typically requires access to benchmark datasets that exhibit the same light curve with and without obstructing noise. Several methods for simulating stellar variability have been proposed for the construction of such benchmark datasets. However, while such methods have been widely used in testing transit method detection algorithms in the past, it is not very well known how such simulations compare to real recorded light curves - a fact that might be contributed to the lack of large databases of stellar light curves for comparisons at that time. With the increasing amount of light curve data now available due to missions such as Kepler, I have here undertaken such a comparison of synthetic and real light curves for one particular method that simulates stellar variability based on scaled power spectra of the Sun’s flux variations. Conducting the respective comparison also in terms of estimated power spectra of real and simulated light curves, I have revealed that the two datasets exhibit substantial differences in average power, with the synthetic power spectra having generally a lower power and also lacking certain distinct power peaks present in the real light curves. The results of this study suggest that scaled power spectra of solar variability alone might be insufficient for light curve simulations and that more work will be required to understand the origin and relevance of the observed power peaks in order to improve on such light curve models.

A potential characterization tool for printer quality is the power spectral density (PSD) analysis of flat-field printer outputs. This thesis explains the relationship between the PSD and characteristics of printer defects using examples of scanned printer outputs. In addition, a protocol is also presented for scanning flat fields and performing a PSD analysis. The protocol considers sampling and windowing issues to best focus on defects or quality issues of interest. The main objective of this work is to determine the interactive relationships of print defect patterns such as graininess, streaking, and banding under flat-field hardcopy outputs. The additive and multiplicative models are considered for describing the interaction between printer defects. Simulated print defect patterns and metrics base on the PSD are used to demonstrate the patterns generated by multiplicative and additive processes. These results are compared the PSD of actual flat-field prints from digital printers to draw conclusion concerning actual artifact interaction. For all defects examined the additive model is shown to be a good model of the interactions between printer defects.

A survey of the literature of grinding and surface texture shows the influence of dressing and wear on surfaces involved in the process and the advantages of stylus profilometry for data collection from both grinding wheels and ground surfaces. Statistical analysis is favoured for surface profile characterization and, of the various parameters used, power spectral density alone offers some prospect of effective comparison between these surfaces. Work on grinding with single crystals of natural corundum was eventually discontinued in favour of experiments with conventional bonded grinding wheels subjected to a dressing operation and some wear in grinding steel surfaces. Statistical parameters representing the surfaces are computed using data obtained from profilograms. Results in terms of power spectral density are presented showing progressive improvement following upon developments in apparatus and methods which facilitated the use of larger surface profile samples. Transfer functions are used to relate power spectra representing corresponding pairs of surfaces. The significance of power spectral density applied to surface profile characterization is discussed and, in this context, it is suggested that these should be described as variance spectra. Attention is drawn to certain disadvantages of variance spectra applied to grinding wheel and ground surface profiles. Methods designed to improve presentation of variance spectra lead to development of a proposed new and more suitable spectrum in which density of standard deviation of surface profile ordinates with respect to frequency is plotted against frequency. Transfer functions calculated from related pairs of these standard deviation spectra show a strong linear correlation with frequency and offer prospects of convenient comparison between the profiles of the various surfaces involved in grinding.

Transcranial direct current stimulation (TDCS) allows for the noninvasive modulation of cortical activity. In this study, the effects of cathodal and anodal TDCS treatment on baseline activity in the motor cortex of rats were investigated via translaminar electroencephalogram (EEG) recording and power spectral density analysis. Treatment with low intensity anodal TDCS for five minutes was found to increase delta and theta frequency cortical activity during and for up to five minutes following treatment. This study also assessed the interaction of TDCS with the phenomenon of cortical spreading depression (CoSD), which has been implicated in numerous disease states, including migraine and stroke. TDCS treatment was given concurrently with induction of CoSD via administration of potassium chloride to the surface of the dura. The presence of the spreading depression event, a characteristic low frequency wave observed to travel outwards from the point of CoSD induction and downwards through the cortex, was used as a proxy measure for the occurrence of CoSD. It was observed that animals treated with cathodal TDCS exhibited fewer spreading depression events relative to those treated with anodal TDCS or those receiving sham treatment. In this study, animals were segregated into groups that exhibited stimulus artifact during TDCS treatment and those that did not. Stimulus artifact was defined as a characteristic alpha and/or beta frequency activity spike lasting throughout and not longer than the period of stimulation. Those animals receiving TDCS without exhibiting stimulus artifact were considered for the purposes of this study to not have received proper TDCS treatment, and acted as a sham treatment group. Because salient differences emerged between the stimulus artifact positive and stimulus artifact negative groups, this study suggests that the presence of stimulus artifact could be used as a proxy measure for successful TDCS dosage.

abstract: Recent new experiments showed that wide-field imaging at millimeter scale is capable of recording hundreds of neurons in behaving mice brain. Monitoring hundreds of individual neurons at a high frame rate provides a promising tool for discovering spatiotemporal features of large neural networks. However, processing the massive data sets is impossible without automated procedures. Thus, this thesis aims at developing a new tool to automatically segment and track individual neuron cells. The new method used in this study employs two major ideas including feature extraction based on power spectral density of single neuron temporal activity and clustering tree to separate overlapping cells. To address issues associated with high-resolution imaging of a large recording area, focused areas and out-of-focus areas were analyzed separately. A static segmentation with a fixed PSD thresholding method is applied to within focus visual field. A dynamic segmentation by comparing maximum PSD with surrounding pixels is applied to out-of-focus area. Both approaches helped remove irrelevant pixels in the background. After detection of potential single cells, some of which appeared in groups due to overlapping cells in the image, a hierarchical clustering algorithm is applied to separate them. The hierarchical clustering uses correlation coefficient as a distance measurement to group similar pixels into single cells. As such, overlapping cells can be separated. We tested the entire algorithm using two real recordings with the respective truth carefully determined by manual inspections. The results show high accuracy on tested datasets while false positive error is controlled within an acceptable range. Furthermore, results indicate robustness of the algorithm when applied to different image sequences. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

A large-area electronics (LAE) strain sensor, termed soft elastomeric capacitor (SEC), has shown great promise in fatigue crack monitoring. The SEC is capable to monitor strain changes over a large structural surface and undergo large deformations under cracking. Previous tests verified that the SEC can detect and localize fatigue cracks under low-cycle fatigue loading. In this paper, we further investigate the SEC's capability for monitoring high-cycle fatigue cracks, which are commonly seen in steel bridges. The peak-to-peak amplitude (pk-pk amplitude) of the SEC measurement is proposed as an indicator of crack growth. This technique is is robust and insensitive to long-term capacitance drift. To overcome the difficulty of identifying the pk-pk amplitude in time series due to high signal-to-noise ratio, a signal processing method is established. This method converts the measured SEC capacitance and applied load to power spectral densities (PSD) in the frequency domain, such that the pk-pk amplitudes of the measurements can be accurately extracted. Finally, the performance of this method is validated using a fatigue test of a compact steel specimen equipped with a SEC. Results show that the crack growth under high-cycle fatigue loading can be successfully monitored using the proposed signal processing method.

As vehicle testing on existing vehicles is both time and resource consuming, the work of testing safety algorithms on vehicle is desired to be made more efficient. Therefore the goal of this thesis is to study and develop a vehicle simulation model that can simulate desired dynamics of existing and non-existing vehicles. The developed model consist of two areas of application: slow dynamics and vibrational dynamics. These areas are developed and validated using different methods, but as a part of the simulator, they are to be simulated together. For the slow, low frequency, vehicle motion, a three state transient motion model is derived and examined. The possibility of parametrisation is studied and performed using prediction error minimisation. For the vibration, high frequency model, a combination of a linear quarter car model with wheel motion is used to estimate road vibration characteristics. The modelled road is used to simulate the vehicle behaviour. The suggested methods regarding the vibration modelling and road estimation are performed using power spectral density as the road is not known determinately. Wheel speeds are used to study the power spectral densities as they are available at high sampling frequencies. The available tools and sensors used during this thesis are limited to existing vehicle sensors and GPS signals. The effect of this limitation is studied and the results are discussed.

Hurricanes are one of the deadliest and costliest natural hazards affecting the Gulf coast and Atlantic coast areas of the United States. An effective way to minimize hurricane damage is to strengthen structures and buildings. The investigation of surface level hurricane wind behavior and the resultant wind loads on structures is aimed at providing structural engineers with information on hurricane wind characteristics required for the design of safe structures. Information on mean wind profiles, gust factors, turbulence intensity, integral scale, and turbulence spectra and co-spectra is essential for developing realistic models of wind pressure and wind loads on structures. The research performed for this study was motivated by the fact that considerably fewer data and validated models are available for tropical than for extratropical storms. Using the surface wind measurements collected by the Florida Coastal Monitoring Program (FCMP) during hurricane passages over coastal areas, this study presents comparisons of surface roughness length estimates obtained by using several estimation methods, and estimates of the mean wind and turbulence structure of hurricane winds over coastal areas under neutral stratification conditions. In addition, a program has been developed and tested to systematically analyze Wall of Wind (WoW) data, that will make it possible to perform analyses of baseline characteristics of flow obtained in the WoW. This program can be used in future research to compare WoW data with FCMP data, as gust and turbulence generator systems and other flow management devices will be used to create WoW flows that match as closely as possible real hurricane wind conditions. Hurricanes are defined as tropical cyclones for which the maximum 1-minute sustained surface wind speeds exceed 74 mph. FCMP data include data for tropical cyclones with lower sustained speeds. However, for the winds analyzed in this study the speeds were sufficiently high to assure that neutral stratification prevailed. This assures that the characteristics of those winds are similar to those prevailing in hurricanes. For this reason in this study the terms tropical cyclones and hurricanes are used interchangeably.

For each generation of electronic equipment there is a trend towards higher power den-sities. Increased heat generation is an undesired consequence that the thermal design unit in a company must handle. The goal of thermal design engineer/unit is to utilizethe same volume to more efficiently transfer more heat from the equipment. This can bedone by exploring more complex and advanced heat sink geometries, optimizing the finshapes and so on. The new prototypes developed will be tested for their reliability and endurance in special chambers called climate chambers, that simulate desired environ-ments. The measurements by thermal design teams in these kind of climate chambers are mainly of outdoor products, whose cooling is based on natural convection. Forcedcooling using fans is optional for these outdoor products. The climate chambers in general provides temperature measurement as the outputto the analysis, though there are other important parameters that define the operationalfunctionality of an equipment. The ability to visualize the flow characteristics duringthe process of testing is a valuable aid in the design process. A virtual/CFD form of thephysical climate chamber (CC) would empower the design process, while alleviating theusage of the climate chambers for such analyses. CFD offers a wide range of capabilitiesthat lets the user change the boundary conditions with great ease compared to that ofthe experimental setup. The numerical model developed in this thesis project provides results, that help inunderstanding the physics involved in fluid flow inside the physical climate chamber.Turbulence quantification of the flow is the main aim of this thesis project, which wouldbe resourceful in future works. Experiments are conducted inside the climate chamber, in order to aid the construction of numerical model as well as serve as source of vali-dation for the numerical results. Laminar transient case simulations are preferred over use of any turbulence models, to limit any kind of predictions made by these turbulencemodels. Integral length scales and turbulence intensities are compared and reason fordiscrepancies are addressed. The results from the comparisons show that, the numerical model emulates physicsof actual flow inside the climate chamber. However, there are many factors that directlyaffect the results, making it difficult to precisely quantify the error, within the time periodof this thesis project.