Дисертації з теми "Bispectrums"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Bispectrums.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-36 дисертацій для дослідження на тему "Bispectrums".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Жемчужкіна, Т. В., and Т. В. Носова. "Construction of bispectra for PCG signals." Thesis, НТУ «ХПІ», 2021. https://openarchive.nure.ua/handle/document/17555.
Повний текст джерелаАнотація:
To construct bispectra for separate segments of PCG such as sounds and murmurs we applied segmentation method based on averaged Shannon envelope. We got bispectrums of sounds and murmurs for different signals: normal and pathological. It can be seen that bispectra are non-zero, so signals are non-Gaussian. There is phase coupling between each two frequencies for each bispectrum. And also, the patterns for bispectra for each person are different in all groups.
2
Cole, Zachary K. "Radar target recognition using bispectrum correlation." Thesis, Monterey, Calif. : Naval Postgraduate School, 2007. http://bosun.nps.edu/uhtbin/hyperion-image.exe/07Jun%5FCole.pdf.
Повний текст джерелаАнотація:
Thesis (M.S. in Physics)--Naval Postgraduate School, June 2007.Thesis Advisor(s): Brett Borden. "June 2007." Description based on title screen as viewed on July 31, 2007. Includes bibliographical references (p. 79-80). Also available in print.
3
Pike, Cameron M. "Multipath signal detection using the bispectrum." Ohio : Ohio University, 1990. http://www.ohiolink.edu/etd/view.cgi?ohiou1183467926.
Повний текст джерела
4
Fergusson, J. "Primordial non-Gaussianity and the CMB bispectrum." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598987.
Повний текст джерелаАнотація:
In this thesis we will present a comprehensive set of formalisms for comparing, evolving, and constraining primordial non-Gaussian models through the CMB bispectrum. First, we introduce the idea of a shape function for characterising the primordial non-Gaussianity. The shape function can also be used to construct a correlator between the models which we use to group the space of possible models into four main classes: equilateral, squeezed, flattened, and scale dependent. Next, we use a common property of the shape function to create a method for calculating, without approximation, the CMB bispectrum from a general primordial model. There are two techniques we use to speed up the calculation. The first is to use the flat sky approximation for large l, and the second is to exploit the smoothness of the reduced bispectrum to calculate the bispectrum first on a sparse grid then interpolate to obtain the remaining points. We then discuss methods for calculating estimators by decomposing the bispectrum, either today or at primordial times, into the product of eigenmodes. First we deal with the primordial bispectrum and describe how the decomposition can be used to both constrain primordial models and to estimate the primordial bispectrum from observations. Then we repeat the analysis for the CMB bispectrum and describe how this process can be used to constrain models, but this time allowing for the inclusion of late time effects. It also presents a method for generating maps with an arbitrary bispectrum and power spectrum.
5
Yankelevich, Victoria [Verfasser]. "Cosmology with the galaxy bispectrum / Victoria Yankelevich." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1200020030/34.
Повний текст джерела
6
Ambrogi, Federico. "Bispectrum of cosmological models with massive neutrinos." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7429/.
Повний текст джерелаАнотація:
Uno dei più importanti campi di ricerca che coinvolge gli astrofisici è la comprensione della Struttura a Grande Scala dell'universo. I principi della Formazione delle Strutture sono ormai ben saldi, e costituiscono la base del cosiddetto "Modello Cosmologico Standard".
Fino agli inizi degli anni 2000, la teoria che spiegava con successo le proprietà statistiche dell'universo era la cosiddetta "Teoria Perturbativa Standard". Attraverso simulazioni numeriche e osservazioni di qualità migliore, si è evidenziato il limite di quest'ultima teoria nel descrivere il comportamento dello spettro di potenza su scale oltre il regime lineare.
Ciò spinse i teorici a trovare un nuovo approccio perturbativo, in grado di estendere la validità dei risultati analitici. In questa Tesi si discutono le teorie "Renormalized Perturbation Theory"e"Multipoint Propagator".
Queste nuove teorie perturbative sono la base teorica del codice BisTeCca, un codice numerico originale che permette il calcolo dello spettro di potenza a 2 loop e del bispettro a 1 loop in ordine perturbativo. Come esempio applicativo, abbiamo utilizzato BisTeCca per l'analisi dei bispettri in modelli di universo oltre la cosmologia standard LambdaCDM, introducendo una componente di neutrini massicci.
Si mostrano infine gli effetti su spettro di potenza e bispettro, ottenuti col nostro codice BisTeCca, e si confrontano modelli di universo con diverse masse di neutrini.
7
Pettinari, Guido Walter. "The intrinsic bispectrum of the Cosmic Microwave Background." Thesis, University of Portsmouth, 2013. https://researchportal.port.ac.uk/portal/en/theses/the-intrinsic-bispectrum-of-the-cosmic-microwave-background(ce62a4e8-625f-4c84-9e0c-821df12cba10).html.
Повний текст джерелаАнотація:
Cosmology, intended as the study of the origin and evolution of the Universe and its components, has advanced from being a philosophical discipline to a data-driven science. Much of this progress was achieved in the last few decades thanks to the wealth of cosmological data from Earth and space-based experiments. The abundance of observational constraints has considerably narrowed the space for theoretical speculation, to the point that now most of the cosmological community agrees on a standard model of cosmology. A crucial assumption of this model is that the structure observed in the Universe, such as planets, stars and galaxies, can be ultimately traced back to tiny density perturbations in the early Universe. Therefore, a huge theoretical and experimental effort is being made by cosmologists and particle physicists to gain insight of the mechanism of generation of these primordial fluctuations, which remains still largely unknown. The bispectrum of the cosmic microwave background (CMB) has been recently recognised as a powerful probe of this mechanism, as it is sensitive to the non-Gaussian features in the seed fluctuations. To access this information, however, it is crucial to model the non-linear evolution of the CMB between the formation of the initial fluctuations and its observation, which results in the emergence of an intrinsic bispectrum. The main purpose of this thesis is to quantify the intrinsic bispectrum and compute the bias it induces on the primordial signal. To do so, we develop SONG, a new and efficient code for solving the second-order Einstein-Boltzmann equations, and use it to estimate the intrinsic CMB non-Gaussianity arising from the non-linear evolution of density perturbations. The full calculation involves contributions from recombination and less tractable ones from terms integrated along the line of sight. We investigate the bias that this intrinsic bispectrum implies for searches of primordial non-Gaussianity. We find that the inclusion or omission of certain line of sight terms can make a large impact. When including all physical effects but lensing and time-delay, we find that the contamination from the intrinsic bispectrum generally leads to a small bias in the estimates of non-Gaussianity, which is good news for the prospect of using cosmic microwave background data to probe primordial non-Gaussianity. The intrinsic non-Gaussianity can be searched for directly, using the predicted signal as a template; our calculations suggest this signal is just beyond what is possible with the Planck CMB survey, with a signal-to-noise rising to unity only for an angular resolution of `max = 3000.
8
Jolicoeur, Sheean. "The observed bispectrum for SKA and other galaxy surveys." University of the Western Cape, 2019. http://hdl.handle.net/11394/6792.
Повний текст джерелаАнотація:
Philosophiae Doctor - PhDNext-generation galaxy surveys will usher in a new era of high precision cosmology. They will increasingly rely on the galaxy bispectrum to provide improved constraints on the key parameters of a cosmological model to percent level or even beyond. Hereby, it is imperative to understand the theory of the galaxy bispectrum to at least the same level of precision. By this, we mean to include all the general relativistic projection effects arising from observing on the past lightcone, which still remains a theoretical challenge. This is because unlike the galaxy power spectrum, the galaxy bispectrum requires these lightcone corrections at second-order. For the rst time, this PhD project looks at all the local relativistic lightcone e ects in the galaxy bispectrum for a at Friedmann-Lemaitre-Robertson-Walker Universe, giving full details on the second-order scalars, vectors and tensors. These lightcone effects are mostly Doppler and gravitational potential contributions. The vector and tensor modes are induced at second order by scalars. We focus on the squeezed shapes for the monopole of the galaxy bispectrum because non-Gaussianity of the local form shows high signatures for these triangular con gurations. In the exact squeezed limit, the contributions from the vectors and tensors vanish. These relativistic projection effects, if not included in the analysis of observations, can be mistaken for primordial non-Gaussianity. For future surveys which will probe equality scales and beyond, all the relativistic corrections will need to be considered for an accurate measurement of primordial non-Gaussianity.
9
Pearson, Ruth. "CMB lensing : polarization, large-scale structure and the primordial bispectrum." Thesis, University of Sussex, 2014. http://sro.sussex.ac.uk/id/eprint/48418/.
Повний текст джерелаАнотація:
Gravitational lensing of photons in the Cosmic Microwave Background (CMB) can be described by an integrated potential along the line of sight, the CMB lensing potential. Covariances in maps of the CMB are generated by the lensing effect, and are used to reconstruct the lensing potential itself, which is a useful probe of the matter distribution. The CMB lensing potential has been measured to high significance with CMB temperature data. However, signal to noise for lensing reconstruction from CMB polarization data is expected to be much better due to the presence of the lensing B-mode. Upcoming data from ground based CMB polarization instruments will provide high resolution maps over small patches of the sky. This will provide much better lensing reconstruction, but also presents data analysis challenges. This thesis begins with an introduction to the field of CMB lensing and CMB lensing reconstruction. The second chapter details the biases present in reconstructing the lensing potential from CMB polarization maps considering first the full sky, and then small patches of sky. It also shows that using the pure-B mode formalism for the CMB polarization leads to improved lensing reconstruction over the naive case on the cut sky. Given the upcoming improvement in the CMB lensing reconstruction, it is expected that cross-correlations of the CMB lensing with other structure tracers, such as galaxies, will yield improved information for cosmology. It is also expected that the CMB lensing will become useful to help constrain uncertainties in the galaxy power spectrum, and provide information on the linear galaxy bias and redshift distribution. The third chapter of the thesis forecasts the power of cross correlation science for a number of galactic and non-galactic parameters. Finally, the CMB lensing effects the level of non-Gaussianity observed in the CMB. The fourth chapter of the thesis is a study of the lensing effect on the primordial squeezed bispectrum. We conclude in the fifth chapter.
10
Lin, Tsu-Shiuan. "Accelerating radio transient detection using the Bispectrum algorithm and GPGPU." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/21198.
Повний текст джерелаАнотація:
Modern radio interferometers such as those in the Square Kilometre Array (SKA) project are powerful tools to discover completely new classes of astronomical phenomena. Amongst these phenomena are radio transients. Transients are bursts of electromagnetic radiation and is an exciting area of research as localizing pulsars (transient emitters) allow physicists to test and formulate theories on strong gravitational forces. Current methods for detecting transients requires an image of the sky to be produced at every time step. Since interferometers have more information available to them, the computational demands for producing images becomes infeasible due to the larger data sets provided by larger interferometers. Law and Bower (2012) formulated a different approach by using a closure quantity known as the "bispectrum": the product of visibilities around a closed loop of antennae. The proposed algorithm has been shown to be easily parallelized and suitable for Graphics processing units (GPUs).Recent advancements in the field of many core technology such as GPUs has demonstrated significant performance enhancements to many scientific applications. A GPU implementation of the bispectrum algorithm has yet to be explored. In this thesis, we present a number of modified implementations of the bispectrum algorithm, allowing both instruction-level and data-level parallelism. Firstly, a multi-threaded CPU version is developed in C++ using OpenMP and then compared to a GPU version developed using Compute Unified Device Architecture (CUDA).In order to verify validity of the implementations presented, the implementations were firstly run on simulated data created from MeqTrees: a tool for simulating transients developed by the SKA. Thereafter, data from the Karl Jansky Very Large Array (JVLA) containing the B0355+54pulsar was used to test the implementation on real data. This research concludes that the bispectrum algorithm is well suited for both CPU and GPU implementations as we achieved a 3.2x speed up on a 4-core multi-threaded CPU implementation over a single thread implementation. The GPU implementation on a GTX670, achieved about a 20 times speed-up over the multi-threaded CPU implementation. These results show that the bispectrum algorithm will open doors to a series of efficient transient surveys suitable for modern data-intensive radio interferometers.
11
Lazanu, Andrei. "The power spectrum and bispectrum of inflation and cosmic defects." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/256999.
Повний текст джерелаАнотація:
Much of the recent progress in cosmology has come from studying the power spectrum of the cosmic microwave background (CMB). The latest results from the Planck satellite confirmed that the inflationary paradigm with the $\Lambda$CDM six-parameter model provides a very good description of the observed structures in the Universe. Even so, additional parameters, such as cosmic defects, are still allowed by current observational data. Additionally, many of the inflationary models predict a significant departure from Gaussianity in the distribution of primordial perturbations. Higher order statistics, such as the bispectrum, are required to test and constrain such models. The late-time distribution of matter in the Universe - large-scale structure (LSS) - contains much more information than the CMB that has not yet been used. In this thesis, we look at both problems: the effects of cosmic defects, in particular cosmic strings and domain walls on the CMB power spectrum through numerical simulations, and the dark matter bispectrum of large-scale structure. Topological defects are predicted by most inflationary theories involving symmetry breaking in the early Universe. In this thesis we study the effects of cosmic strings and domain walls on the CMB by determining their power spectrum. We use Nambu-Goto and field theory simulations for cosmic strings and domain walls respectively, and we determine the power spectra they produce with a modified Einstein-Boltzmann solver sourced by unequal time correlators from components of the energy-momentum tensor of the defects. We use these spectra together with CMB likelihoods to obtain constraints on the energy scales of formation of the cosmic defects, finding $G\mu/c^{2} < 1.29 \times 10^{−7}$ and $\eta < 0.93$ MeV (at 95% confidence level) for cosmic strings and domain walls respectively, when using the Planck satellite likelihoods. For the matter bispectrum of LSS, we compare different perturbative and phenomenological models with measurements from $N$-body simulations by using shape and amplitude correlators and we determine on which scales and for which redshifts they are accurate. We propose a phenomenological ‘three-shape’ model, based on the fundamental shapes we have observed by studying the halo model that are also present in the simulations. When calibrated on the simulations, this model accurately describes the bispectrum on all scales and redshifts considered, providing a prototype bispectrum HALOFIT-like methodology that could be used to describe and test parameter dependencies.
12
Wear, Steven M. "Shift-invariant image reconstruction of speckle-degraded images using bispectrum estimation /." Online version of thesis, 1990. http://hdl.handle.net/1850/11219.
Повний текст джерела
13
Freeman, Jonathan Dennis. "Estimation of astronomical images from the bispectrum of atmospherically distorted infrared data." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184939.
Повний текст джерелаАнотація:
The uses of the bispectrum for recovering the images of one-dimensional infrared astronomical speckle data are examined in detail. An analytic model for the bispectral transfer function, the variance, and the covariance of the bispectrum are developed. The models are evaluated by Monte Carlo integration and the results are compared to sample estimates of the same quantities obtained from simulated data. For comparison, the same sample quantities are computed from observed data. The bispectrum is shown to be useful for determining estimates of the object phase. A recursive method which is used to obtain the object phase estimates is introduced. Since the bispectrum provides multiple estimates of each object phase, a number of methods for combining the multiple estimates are developed and compared. Many techniques have been proposed to determine the phase of images which have been atmospherically distorted. Among these techniques are the Knox-Thompson, and the Simple Shift-and-Add algorithms. These methods are compared to the bispectrum via an objective measure which is developed. Optimization techniques are used to great success. A model for the bispectrum of a binary star is developed and fit to the image bispectrum by the Levenberg-Marquardt algorithm for non-linear least squares. The ability of the algorithm to determine binary star parameters from the bispectrum is tested with both simulated and observed data. Since the bispectrum may not always be available, a method is developed which determines binary star parameters from the image Fourier transform. The full set of object phases and moduli are determined by use of the conjugate gradient and conjugate direction algorithms in the last section. Two starting points for each algorithm are employed. The first starting point uses the estimates of the object phases obtained from the recursive bispectrum technique. The second assumes no information is known about the object. The speed of convergence of each algorithm is analyzed and recommendations are made for future use.
14
Clunan, Timothy Peter. "The primordial universe : instantons, the ghost spectrum and the closed universe bispectrum." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608826.
Повний текст джерела
15
Hashimoto, Ichihiko. "Toward a precision cosmological test of gravity from redshift-space bispectrum based on perturbation theory." Kyoto University, 2018. http://hdl.handle.net/2433/232243.
Повний текст джерела
16
Ammermann, Peter A. "Nonlinearity and Overseas Capital Markets: Evidence from the Taiwan Stock Exchange." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28816.
Повний текст джерелаАнотація:
Numerous studies have documented the existence of nonlinearity within various financial time series. But how important of a finding is this? This dissertation examines this issue from a number of perspectives. First, is the nonlinearity that has been found a statistical anomaly that is isolated to a few of the more widely known financial time series or is nonlinearity a statistical regularity inherent in such series? Second, even if nonlinearity is pervasive, does this finding have any practical relevance for finance practitioners or academics?
Using the relatively financially isolated but nonetheless well-traded Taiwan Stock Exchange as a case study, it is found that virtually all of the stocks trading on this exchange exhibit nonlinearity. The pervasiveness of nonlinearity within this market, combined with earlier results from other markets, suggests that nonlinearity is an inherent aspect of financial time series. Furthermore, closer examination of the time-paths of various measures of this nonlinearity via both windowed testing and recursive testing and parameter estimation reveals an additional complication, the possibility of nonstationarity. The serial dependency structures, especially for the nonlinear dependencies, do not appear to be constant, but instead appear to exhibit a number of brief episodes of extremely strong dependencies, followed by longer stretches of relatively quiet behavior. On average, though, these nonlinearities appear with sufficient strength to be significant for the full sample.
Continuing on to examine the relevance of such nonlinearities for empirical work in finance, a variety of conditionally heteroskedastic models were fit to the returns for a subsample Taiwanese stocks, the Taiwanese stock index, and stock indices for other stock markets, including New York, London, Tokyo, Hong Kong, and Singapore. In a majority of cases, such models appear to be successful at filtering out the extant nonlinearity from these series of returns; however, a variety of indicators suggest that these models are not statistically well-specified for these returns, calling into question the inferences obtained from these models. Furthermore, a comparison of the various conditionally heteroskedastic models with each other and with a dynamic linear regression model reveals that, for many of the data series, the inferences obtained from these models regarding the day-of-the-week effect and the extant autocorrelation within the data varied from model to model. This finding suggests the importance of adequately accounting for nonlinear serial dependencies (and of ensuring data stationarity) when studying financial time series, even when other empirical aspects of the data are the focus of attention.Ph. D.
17
Williams, Mark Lawrence. "The use of bispectrum and other higher order statistics in the analysis of one dimensional signals." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/55347.
Повний текст джерелаАнотація:
A huge body of literature has been published on the use of second order statistics in signal processing, mainly through the study of the power spectrum. This is a sensible way to analyse signals since all non-trivial signals possess variance and the second order statistics are simple to calculate. A relatively small amount has been published on the use of higher order statistics and most of this has been produced in the last decade. There are two main reasons for the current surge in interest in the higher order statistics. The first is that the higher order statistics contain information not present in the second order statistics and as a relatively new field there is much to be discovered. The second is that with the availability of powerful computers the effort involved in calculating higher order statistics has been reduced to the level where the rewards justify it. The family of higher order spectra is presented and various problems are examined with reference to the properties of these spectra (more specifically, the second and third-members of the polyspectra family, the bispectrum and trispectrum). The use of the bispectrum is examined to assist the detection of continuous unknown signals in noise. Methods for making full use of the third order statistics of the signal are examined and their potential assessed. In the case of ship noise hidden in ambient sea noise, it was found that although the ship noise possesses significant levels of skewness it is not present at a high enough level to appreciably improve detection. Various aspects of the bispectrum are investigated and complete expressions for the variance and covariance of the bispectral estimate are derived. New tests for stationarity of the sampled and continuous signal are presented. Fault is found with the use of the linear model to simulate samples from non-Gaussian continuous stationary signals. The effects of bandlimiting on the third and fourth order statistics of signals is examined.
18
Wang, Xue. "CARDIO-RESPIRATORY INTERACTION AND ITS CONTRIBUTION IN SYNCOPE." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/254.
Повний текст джерелаАнотація:
A hypothetical causal link between ventilatory regulation of carbon dioxide anddevelopment of syncope during orthostatic challenges is reduction in arterial partialpressure of carbon dioxide and resultant reduction in cerebral blood flow. We performedtwo experiments to investigate the ventilatory sensitivity to carbon dioxide and factorsaffecting cerebral autoregulation (CA). We also studied the nonlinear phase couplingbetween cardio-respiratory parameters before syncope.For experiment one, in 30 healthy adults, we stimulated chemo and baro reflexesby breathing either room-air or room-air with 5 percent carbon dioxide in a pseudorandom binary sequence during supine and 70 degree head up tilt (HUT). Six subjectsdeveloped presyncope during tilt.To determine whether changes in ventilatory control contribute to the observeddecrease in PaCO2 during HUT, we assessed ventilatory dynamic sensitivity to changesin PaCO2 during supine and 70 degrees HUT. The sensitivity of the ventilatory controlsystem to perturbations in end tidal carbon dioxide increased during tilt.To investigate nonlinear phase coupling between cardio-respiratory parametersbefore syncope, bispectra were estimated and compared between presyncopal andnon-presyncopal subjects. Our results indicate that preceding presyncope, nonlinearphase coupling is altered by perturbations to baro and chemo reflexes.To investigate the effects of gender in CA, we selected 10 men and 10age-matched women and used spectral analysis to compare differences in CA betweenmen and women. Our results showed that gender-related differences in CA did exist andgender may need to be considered as a factor in investigating CA.To investigate the influence of induced hypocapnia on CA in absence ofventilatory variability, we performed experiment two in which subjects were randomlyassigned to a Control (under normocapnia) or Treatment (under hypocapnia) group. Bothgroups voluntarily controlled their breathing pattern yet two groups breathed in air withdifferent levels of carbon dioxide. Our results show that changes in mean blood pressureat middle cerebral artery level were less transferred into mean cerebral blood flow in theTreatment group than in the Control group, suggesting better CA under hypocapniarelative to under normocapnia.
19
Yoo, Byungseok. "Practical Aspects of Assessing Nonlinear Ultrasonic Response of Cyclically Load 7075-T6 Aluminum." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36335.
Повний текст джерелаАнотація:
The ultrasonic NDE technique to characterize the ultrasonic nonlinear response of the cyclically load 7075-T6 aluminum is described in this thesis. In order to estimate the nonlinear relation of the ultrasonic waves due to material fatigue damage or degradation, the spectral analysis techniques such as the power spectrum, bispectrum, and bicoherence spectrum are applied. The ultrasonic nonlinearity parameters by Cantrell and Jhang are introduced and presented as a function of the material fatigue growth, the number of fatigue cycles. This thesis presents the effectiveness of the bispectral analysis for evaluating the nonlinear aspects of the ultrasonic wave propagation. The results show that the nonlinearity parameters by Cantrell and Jhang are responsive to the output amplitude of the received signal and vary for the various materials, and independent of the input frequency and the ultrasonic wave propagation distance. By using the bispectral analysis tools, particularly the bicoherence spectrum, the increase of the coupling levels between the fundamental, its harmonic, and subharmonic frequency components is presented as the number of fatigue cycles is increased. This thesis suggests that the application of the bicoherence spectrum based on the nonlinear wave coupling relations be more effective for estimating the level of the material fatigue life.Master of Science
20
Jaimes, Rafael. "Spatiotemporal Organization of Atrial Fibrillation Using Cross-Bicoherence with Surrogate Data." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/828.
Повний текст джерелаАнотація:
Atrial fibrillation (AF) is a troublesome disease often overlooked by more serious myocardial infarctions. Up until now, there has been very little or no use of high order spectral techniques in order to evaluate the organization of the atrium during AF. Cross-bicoherence algorithm can be used alongside a surrogate data threshold in order to determine significant phase coupling interactions, giving rise to an organizational metric. This proposed algorithm is used to show rotigaptide, a gap junction coupling drug, significantly increases the organization of the atria during episodes of AF due to improvement of cell-to-cell coupling.
21
Su, Shi Chun. "Post-inflationary non-Gaussianities on the cosmic microwave background." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/249054.
Повний текст джерелаАнотація:
The cosmic microwave background (CMB) provides unprecedented details about the history of our universe and helps to establish the standard model in modern cosmology. With the ongoing and future CMB observations, higher precision can be achieved and novel windows will be opened for studying different phenomena. Non-Gaussianity is one of the most exciting effects which fascinate many cosmologists. While numerous alternative inflationary models predict detectable primordial non-Gaussianities generated during inflation, the single-field slow-roll inflation of the standard model is known to produce negligible non-Gaussianities. However, post-inflationary processes guarantee the generation of non-Gaussianities through the nonlinear evolution of our universe after inflation, regardless of the underlying inflationary theory. These non-Gaussianities not only may contaminate the potential primordial non-Gaussian signals, but also may offer independent tests for late-time physics (such as General Relativity). Therefore, it is of great interest to study them quantitatively. In this thesis, we will study the post-inflationary non-Gaussianities in two main aspects. First, we calculate the CMB bispectrum imprinted by the 2nd-order perturbations during recombination. We carry out a numerical calculation including all the dominant effects at recombination and separate them consistently from the late-time effects. We find that the recombination bispectrum is subdominant compared to the ISW-lensing bispectrum. Although the effect will not be detectable for the Planck mission, its signal-to-noise is large enough that they present themselves as systematics. Thus, it has to be taken into account in future experiments. Second, we formulate the lensing, redshift and time-delay effects through the Boltzmann equation. The new formalism allows us to explicitly list out all the approximations implied in the canonical remapping approach. In particular, we quantify the correction of the CMB temperature power spectrum from the lens-lens couplings and confirm that the correction is small.
22
Ong, Hannah Chien Leing. "Virus recognition in electron microscope images using higher order spectral features." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16186/.
Повний текст джерелаАнотація:
Virus recognition by visual examination of electron microscope (EM) images is time consuming and requires highly trained and experienced medical specialists. For these reasons, it is not suitable for screening large numbers of specimens. The objective of this research was to develop a reliable and robust pattern recognition system that could be trained to detect and classify different types of viruses from two-dimensional images obtained from an EM. This research evaluated the use of radial spectra of higher order spectral invariants to capture variations in textures and differences in symmetries of different types of viruses in EM images. The technique exploits invariant properties of the higher order spectral features, statistical techniques of feature averaging, and soft decision fusion in a unique manner applicable to the problem when a large number of particles were available for recognition, but were not easily registered on an individual basis due to the low signal to noise ratio. Experimental evaluations were carried out using EM images of viruses, and a high statistical reliability with low misclassification rates was obtained, showing that higher order spectral features are effective in classifying viruses from digitized electron micrographs. With the use of digital imaging in electron microscopes, this method can be fully automated.
23
Ojansivu, V. (Ville). "Blur invariant pattern recognition and registration in the Fourier domain." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514292552.
Повний текст джерелаАнотація:
Abstract
Pattern recognition and registration are integral elements of computer vision, which considers image patterns. This thesis presents novel blur, and combined blur and geometric invariant features for pattern recognition and registration related to images. These global or local features are based on the Fourier transform phase, and are invariant or insensitive to image blurring with a centrally symmetric point spread function which can result, for example, from linear motion or out of focus.
The global features are based on the even powers of the phase-only discrete Fourier spectrum or bispectrum of an image and are invariant to centrally symmetric blur. These global features are used for object recognition and image registration. The features are extended for geometrical invariances up to similarity transformation: shift invariance is obtained using bispectrum, and rotation-scale invariance using log-polar mapping of bispectrum slices. Affine invariance can be achieved as well using rotated sets of the log-log mapped bispectrum slices. The novel invariants are shown to be more robust to additive noise than the earlier blur, and combined blur and geometric invariants based on image moments.
The local features are computed using the short term Fourier transform in local windows around the points of interest. Only the lowest horizontal, vertical, and diagonal frequency coefficients are used, the phase of which is insensitive to centrally symmetric blur. The phases of these four frequency coefficients are quantized and used to form a descriptor code for the local region. When these local descriptors are used for texture classification, they are computed for every pixel, and added up to a histogram which describes the local pattern. There are no earlier textures features which have been claimed to be invariant to blur. The proposed descriptors were superior in the classification of blurred textures compared to a few non-blur invariant state of the art texture classification methods.
24
Erturk, Alp. "Rotation, Scale And Translation Invariant Automatic Target Recognition Using Template Matching For Satellite Imagery." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611434/index.pdf.
Повний текст джерелаАнотація:
In this thesis, rotation, scale and translation (RST) invariant automatic target recognition (ATR) for satellite imagery is presented. Template matching is used to realize the target recognition. However, unlike most of the studies of template matching in the literature, RST invariance is required in our problem, since most of the time we will have only a small number of templates of each target, while the targets to be recognized in the scenes will have various orientations, scaling and translations. RST invariance is studied in detail and implemented with some of the competing methods in the literature, such as Fourier-Mellin transform and bipectrum combined with log-polar mapping. Phase correlation and normalized cross-correlation are used as similarity metrics. Encountered drawbacks were overcome with additional operations and modifications of the algorithms. ATR using reconstruction of the target image with respect to the template, based on bispectrum, log-polar mapping and phase correlation outperformed the other methods and successful recognition was realized for various target types, especially for targets on relatively simpler backgrounds, i.e. containing little or no other objects.
25
Strange, Andrew Darren. "Robust thin layer coal thickness estimation using ground penetrating radar." Queensland University of Technology, 2007. http://eprints.qut.edu.au/16356/.
Повний текст джерелаАнотація:
One of the most significant goals in coal mining technology research is the automation of underground coal mining machinery. A current challenge with automating underground coal mining machinery is measuring and maintaining a coal mining horizon. The coal mining horizon is the horizontal path the machinery follows through the undulating coal seam during the mining operation. A typical mining practice is to leave a thin remnant of coal unmined in order to maintain geological stability of the cutting face. If the remnant layer is too thick, resources are wasted as the unmined coal is permanently unrecoverable. If the remnant layer is too thin, the product is diluted by mining into the overburden and there is an increased risk of premature roof fall which increases danger. The main challenge therefore is to develop a robust sensing method to estimate the thickness of thin remant coal layers. This dissertation addresses this challenge by presenting a pattern recognition methodology to estimate thin remnant coal layer thickness using ground penetrating radar (GPR). The approach is based upon a novel feature vector, derived from the bispectrum, that is used to characterise the early-time segment of 1D GPR data. The early-time segment is dominated by clutter inherent in GPR systems such as antenna crosstalk, ringdown and ground-bounce. It is common practice to either time-gate the signal, disregard the clutter by rendering the early-time segment unusable, or configure the GPR equipment to minimise the clutter effects which in turn reduces probing range. Disregarding the early-time signal essentially imposes a lower thickness limit on traditional GPR layer thickness estimators. The challenges of estimating thin layer thickness is primarily due to these inherent clutter components. Traditional processing strategies attempt to minimise the clutter using pre-processing techniques such as the subtraction of a calibration signal. The proposed method, however, treats the clutter as a deterministic but unknown signal with additive noise. Hence the proposed approach utilises the energy from the clutter and monitors change in media from subtle changes in the signal shape. Two complementary processing methods important to horizon sensing have been also proposed. These methods, near-surface interface detection and antenna height estimation, may be used as pre-validation tools to increase the robustness of the thickness estimation technique. The proposed methods have been tested with synthetic data and validated with real data obtained using a low power 1.4 GHz GPR system and a testbed with known conditions. With the given test system, it is shown that the proposed thin layer thickness estimator and near-surface interface detector outperform the traditional matched filter based processing methods for layers less than 5 cm in thickness. It is also shown that the proposed antenna height estimator outperforms the traditional height estimator for heights less than 7 cm. These new methods provide a means for reliably extending layer thickness estimation to the thin layer case where traditional approaches are known to fail.
26
Pidde, Aleksandra. "Dynamics of the membrane potential: studies of the membrane potential of Jurkat cells using wavelet and wavelet bispectral analysis." Doctoral thesis, Universitat Pompeu Fabra, 2020. http://hdl.handle.net/10803/670401.
Повний текст джерелаАнотація:
Fluctuations are fundamental for living organisms. They arguably result from interactions with the complex, and unpredictable environment, and can often be manifested as temporal variability. The cell must continually resist the external variations in the osmotic pressure by continuous adjustments in the intracellular concentrations. This happens through a highly specialised network of membrane transporters, and is manifested in the dynamics of the membrane potential. The aim of the work presented here is to provide understanding and insight into the dynamics of the free-running membrane potential in nonexcitable cells, based on experimental data. In order to achieve this, first the quantitative comparisons of the average values of the membrane potential and their standard deviations recorded in various conditions are made. The analysis is further extended through the use of the wavelet transform to investigate the time and frequency components of the signal. This work is the first to report an intermittent oscillations in the membrane potential around frequency of 8 mHz but also around frequencies of 0.03, 0.05 or 0.09 Hz. To further understand this dynamics from univariate time series, time-reversibility is investigated and a novel wavelet-bispectral density analysis is developed. The wavelet-bispectral density allows for a formal quantitative, not merely qualitative interpretation of the results of wavelet-bispectral analysis. Finally, the newly developed autowavelet-bispectral analysis is applied to the recordings of the membrane potential. These indicate possible nonlinear couplings between different oscillatory modes in the cellular membrane potential.Les fluctuacions són fonamentals pels éssers vius i probablement siguin el resultat d’interaccions amb un entorn complex i impredictible. Aquest tipus d’activitat es pot manifestar en forma de variabilitat temporal. Les cèl.lules han de resistir contínuament les variacions externes de la pressió osmòtica fent reajustaments continus de les concentracions intracel.lulars. Això és possible gràcies a una xarxa altament especialitzada de transportadors de membrana i dóna lloc a la dinàmica del potencial de membrana. L’objectiu d’aquest treball és proporcionar una millor comprensió de la dinàmica del potencial lliure de membrana en cèl.lules no excitables a partir de dades experimentals. Amb aquest objectiu i en primer lloc, comparem la mitjana i la desviació estàndard del potencial de membrana en diferents condicions de registre. Complementem aquesta anàlisi investigant les components temporo-freqüencials de la senyal mitjançant la transformada wavelet. Aquest és el primer treball on es reporten oscil.lacions intermitents del potencial de membrana amb una freqüència aproximada de 8 mHz, però també al voltant de 0.03, 0.05 i 0.09 Hz. Per entendre millor aquest comportament en el context d’una sèrie temporal univariada, utilitzem el biespectre-wavelet i l’anàlisi de reversibilitat del temps. A més, proposem una nova mesura, la densitat biespectral-wavelet, que permet fer una interpretació quantitativa -i no només qualitativa- dels resultats de l’ànalisi biespectralwavelet. L’aplicació del nou formalisme als registres del potencial de membrana posa de manifest l’existència de possibles acoblaments no lineals entre diferents modes oscil.latoris en el potencial de membrana.
27
Guandalin, Caroline Macedo. "Primordial non-Gaussianities: Theory and Prospects for Observations." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-24092018-155602/.
Повний текст джерелаАнотація:
Early Universe physics leaves distinct imprints on the Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS). The current cosmological paradigm to explain the origin of the structures we see in the Universe today (CMB and LSS), named Inflation, says that the Universe went through a period of accelerated expansion. Density fluctuations that eventually have grown into the temperature fluctuations of the CMB and the galaxies and other structures we see in the LSS come from the quantization of the scalar field (inflaton) which provokes the accelerated expansion. The most simple inflationary model, which contains only one slowly-rolling scalar field with canonical kinetic term in the action, produces a power-spectrum (Fourier transform of the two-point correlation function) approximately scale invariant and an almost null bispectrum (Fourier transform of the three-point correlation function). This characteristic is called Gaussianity, once random fields that follow a normal distribution have all the odd moments null. Yet, more complex inflationary models (with more scalar fields and/or non-trivial kinetic terms in the action, etc) and possible alternatives to inflation have a non-vanishing bispectrum which can be parametrized by a non-linearity parameter f_NL, whose value differs from model to model. In this work we studied the basic ingredients to understand such statements and focused on the observational evidences of this parameters and how the current and upcoming galaxy surveys are able to impose constraints to the value of f_NL with a better accuracy, through the multi-tracer technique, than those obtained by means of CMB measurements.A física do Universo primordial deixa sinais distintos na Radiação Cósmica de Fundo (CMB) e Estrutura em Larga Escala (LSS). O paradigma atual da cosmologia explica a origem das estruturas que vemos hoje (CMB e LSS) através da inflação, teoria que diz que o Universo passou por um período de expansão acelerada. As flutuações de densidade que eventualmente crescem, dando origem às flutuações de temperatura da CMB, às galáxias e outras estruturas que vemos na LSS, provém da quantização do campo escalar (inflaton) que provoca a tal expansão acelerada. O modelo inflacionário mais simples, o qual contém um único campo escalar nas condições de rolamento lento e termo cinético canônico da ação, possui o espectro de potências (transformada de Fourier da função de correlação de dois pontos) aproximadamente invariante de escala e o bispectro (transformada de Fourier da função de correlação de três pontos) aproximadamente nulo. Tal característica é conhecida por Gaussianidade, uma vez que campos aleatórios cuja distribuição é uma normal tem todas as funções de correlação de ordem ímpar nulas. Contudo, modelos inflacionários mais complexos (mais campos escalares, termos cinéticos não-triviais na ação, etc) e alternativas possíveis à inflação possuem um bispectro não nulo, o qual pode ser parametrizado através do parâmetro de não-linearidade f_NL, cujo valor difere de modelo para modelo. Neste trabalho estudamos os ingredientes básicos para entender tais afirmações e focamos nas evidências observacionais desse parâmetro e como os levantamentos de galáxias atuais e futuros podem impor restrições ao valor de f_NL com uma precisão maior, através da técnica de múltiplos traçadores, do que aquelas obtidas com medidas da CMB.
28
Lacasa, Fabien. "Non-Gaussianity and extragalactic foregrounds to the Cosmic Microwave Background." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00955975.
Повний текст джерелаАнотація:
This PhD thesis, written in english, studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB), the latter being one of the golden observables of today's cosmology. In the last decade has emerged research for deviations of the CMB to the Gaussian law, as they would discriminate the models for the generation of primordial perturbations. However the CMB measurements, e.g. by the Planck satellite, are contaminated by several foregrounds. I studied in particular the extragalactic foregrounds which trace the large scale structure of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). I hence describe the statistical tools to characterise a random field : the correlation functions, and their harmonic counterpart : the polyspectra. In particular the bispectrum is the lowest order indicator of NG, with the highest potential signal to noise ratio (SNR). I describe how it can be estimated on data, accounting for a potential mask (e.g. galactic), and propose a method to visualise the bispectrum, which is more adapted than the already existing ones. I then describe the covariance of a polyspectrum measurement, a method to generate non-Gaussian simulations, and how the statistic of a 3D field projects onto the sphere when integrating along the line-of-sight. I then describe the generation of density perturbations by the standard inflation model and their possible NG, how they yield the CMB anisotropies and grow to form the large scale structure of today's universe. To describe this large scale structure, I present the halo model and propose a diagrammatic method to compute the polyspectra of the galaxy density field and to have a simple and powerful representation of the involved terms. I then describe the foregrounds to the CMB, galactic as well as extragalactic. I briefly describe the physics of the thermal Sunyaev-Zel'dovich effect and how to describe its spatial distribution with the halo model. I then describe the extragalactic point-sources and present a prescription for the NG of clustered sources. For the Cosmic Infrared Background (CIB) I introduce a physical modeling with the halo model and the diagrammatic method. I compute numerically the 3D galaxy bispectrum and produce the first theoretical prediction of the CIB angular bispectrum. I show the contributions of the different terms and the temporal evolution of the galaxy bispectrum. For the CIB angular bispectrum, I show its different terms, its scale and configuration dependence, and how it varies with model parameters. By Fisher analysis, I show it allows very good constraints on these parameters, complementary to or better than those coming from the power spectrum. Finally, I describe my work on measuring NG. I first introduce an estimator for the amplitude of the CIB bispectrum, and show how to combine it with similar ones for radio sources and the CMB, for a joint constraint of the different sources of NG. I quantify the contamination of extragalactic point-sources to the estimation of primordial NG ; for Planck it is negligible for the central CMB frequencies. I then describe my measurement of the CIB bispectrum on Planck data ; it is very significantly detected at 217, 353 and 545 GHz with SNR ranging from 5.8 to 28.7. Its shape is consistent between frequencies, as well as the intrinsic amplitude of NG. Ultimately, I describe my measurement of the tSZ bispectrum, on simulations and on Compton parameter maps estimated by Planck, validating the robustness of the estimation thanks to realist foreground simulations. The tSZ bispectrum is very significantly detected with SNR~200. Its amplitude and its scale and configuration dependence are consistent with the projected map of detected clusters and tSZ simulations. Finally, this measurement allows to put a constraint on the cosmological parameters : sigma_8*(Omega_b/0.049)^0.35 = 0.74+/-0.04 in agreement with other tSZ statistics.
29
Wang, Chai-Hong, and 王嘉鴻. "Applications of Bispectrum on Signal Reconstruction and Enhancement." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/48866214757625272581.
Повний текст джерелаАнотація:
碩士大同工學院
電機工程研究所
81
Higherorder spectrum are defined in terms of cumulants therefore are also called cumulant spectrum. In recent years, bispectral analysis has gained its popularity in many application fields because of affordable fast computing facilities and better interpretation and understanting of higher-order statistics. Unlike the power spectrum which contains the Fourier-magnitude information only, the bispectrum contains all the information concerning the Fourier phase and Fourier-magnitude of the signal. To use this property of bispectrum, this research first attempts to investigate methods of bispectrum estimation for finite data. We then use these properties to reconstruct the signal. In addition we discuss methods for signal reconstruction solely from the bispectral phase of a sequence to achieve data reduction.Furthermore, it is known that the Gaussian noise was zero at the higher-order (>2) statistics. We attempt to suppress the Gaussian noise by the characteristic that the third-order moment of the Gaussian noise is zero. From our experimental results, it is found that bispectrum can be used to suppress the Gaussian noise and enhance speech signals.
30
HAN, CHIN-MIN, and 韓治民. "Bispectrum estimation and its applications on speech analysis." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/25030319771966058310.
Повний текст джерела
31
HUANG, JIN-SHENG, and 黃金生. "Study of the relationship between bispectrum and asymmetry." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/74434650853874170013.
Повний текст джерела
32
Karimi, Davood. "Spectral and Bispectral Analysis of Awake Breathing Sounds for Obstructive Sleep Apnea Diagnosis." 2013. http://hdl.handle.net/1993/18327.
Повний текст джерелаАнотація:
The goal of this study was to investigate the potential of breathing sounds recorded during wakefulness for Obstructive Sleep Apnea (OSA) screening and severity estimation. Breathing sounds were recorded from 189 subjects in supine and sitting postures during nose and mouth breathing. Features were extracted from power spectrum and bispectrum of the signals. Data from 70 subjects were used for training. Validation accuracy, specificity, and sensitivity for non-OSA and OSA groups were 78%, 77%, and 82%, respectively. Screening based on six OSA risk factors was less accurate. Parallel classification by both breathing sound features and risk factors had high sensitivity (94%). OSA severity estimation, by classifying subjects into three classes of OSA severity, achieved a maximum validation accuracy of 71%. The results demonstrate the potential of breathing sounds for OSA screening. The proposed method can lead to significant improvements in efficient use of resources such as sleep laboratories.
33
ZHANG, ZHI-GI, and 張智奇. "The determination of modal damping ratios and natural frequencies from bispectrum modeling." Thesis, 1987. http://ndltd.ncl.edu.tw/handle/96862596527620749562.
Повний текст джерела
34
Ke, Chih-Hsiung, and 柯智雄. "Application of Bispectrum in the Impact-Echo Method to Identify Reinforcing Steel Bar and Crack." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/36467730239344065194.
Повний текст джерела
35
Melicherčík, Martin. "Testy linearity v časových řadách." Master's thesis, 2013. http://www.nusl.cz/ntk/nusl-321443.
Повний текст джерелаАнотація:
Title: Testing for linearity in time series Author: Martin Melicherčík Department: Department of Probability and Mathematical Statistics Supervisor: doc. RNDr. Zuzana Prášková, CSc., Department of Probability and Mathematical Statistics Abstract: In the first part of the thesis, a necessary theoretical base from time series analysis is explained, which is consequently used to formulate several tests for linearity. According to variety of approaches the theory includes wide range of knowledge from correlation and spectral analysis and introduces some basic nonlinear models. In the second part, linearity tests are described, classified and compared both theoretically and practically on simulated data from several linear and nonlinear models. At the end, some scripts and hints in R language are introduced that could be used when applying tests to real data. Keywords: linear time series, bispectrum, testing for linearity, nonlinear models
36
Gagnon, David Edward. "Bispectral analysis of nonlinear acoustic propagation." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3177.
Повний текст джерелаАнотація:
Higher-order spectral analysis of acoustical waveforms can provide phase information that is not retained in calculations of power spectral density. In the propagation of high intensity sound, nonlinearity can cause substantial changes in the waveform as frequency components interact with one another. The bispectrum, which is one order higher than power spectral density, may provide a useful measure of nonlinearity in propagation by highlighting spectral regions of interaction. This thesis provides a review of the bispectrum, places it in the context of nonlinear acoustic propagation, and presents spectra calculated as a function of distance for numerically propagated acoustic waveforms. The calculated spectra include power spectral density, quad-spectral density, bispectrum, spatial derivative of the bispectrum, bicoherence, and
skewness function.text