Academic literature on the topic 'Cross spectral coherency analysis'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Cross spectral coherency analysis.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Cross spectral coherency analysis"
1
Maraun, D., and J. Kurths. "Cross wavelet analysis: significance testing and pitfalls." Nonlinear Processes in Geophysics 11, no. 4 (2004): 505–14. http://dx.doi.org/10.5194/npg-11-505-2004.
Full textAbstract:
Abstract. In this paper, we present a detailed evaluation of cross wavelet analysis of bivariate time series. We develop a statistical test for zero wavelet coherency based on Monte Carlo simulations. If at least one of the two processes considered is Gaussian white noise, an approximative formula for the critical value can be utilized. In a second part, typical pitfalls of wavelet cross spectra and wavelet coherency are discussed. The wavelet cross spectrum appears to be not suitable for significance testing the interrelation between two processes. Instead, one should rather apply wavelet coherency. Furthermore we investigate problems due to multiple testing. Based on these results, we show that coherency between ENSO and NAO is an artefact for most of the time from 1900 to 1995. However, during a distinct period from around 1920 to 1940, significant coherency between the two phenomena occurs.
2
Lainscsek, Claudia, Manuel E. Hernandez, Howard Poizner, and Terrence J. Sejnowski. "Delay Differential Analysis of Electroencephalographic Data." Neural Computation 27, no. 3 (2015): 615–27. http://dx.doi.org/10.1162/neco_a_00656.
Full textAbstract:
We propose a time-domain approach to detect frequencies, frequency couplings, and phases using nonlinear correlation functions. For frequency analysis, this approach is a multivariate extension of discrete Fourier transform, and for higher-order spectra, it is a linear and multivariate alternative to multidimensional fast Fourier transform of multidimensional correlations. This method can be applied to short and sparse time series and can be extended to cross-trial and cross-channel spectra (CTS) for electroencephalography data where multiple short data segments from multiple trials of the same experiment are available. There are two versions of CTS. The first one assumes some phase coherency across the trials, while the second one is independent of phase coherency. We demonstrate that the phase-dependent version is more consistent with event-related spectral perturbation analysis and traditional Morlet wavelet analysis. We show that CTS can be applied to short data windows and yields higher temporal resolution than traditional Morlet wavelet analysis. Furthermore, the CTS can be used to reconstruct the event-related potential using all linear components of the CTS.
3
While, James, Andrew Jackson, Dirk Smit, and Ed Biegert. "Spectral analysis of gravity gradiometry profiles." GEOPHYSICS 71, no. 1 (2006): J11—J22. http://dx.doi.org/10.1190/1.2169848.
Full textAbstract:
The gravity gradient tensor (whose components are the second derivatives of the gravitational potential) is a symmetric tensor that, ignoring the constraint imposed by Laplace's equation, contains only six independent components. When measured on a horizontal plane, these components generate, in the spectral domain, six power spectral densities (PSDs) and fifteen cross-spectra. The cross-spectra can be split into two groups: a real group and a pure imaginary group. If the source distribution is statistically stationary, 1D spectra can be found from the 2D spectra via the slice theorem. The PSDs form two power-sum rules that link all gradient components. The power-sum rules, in combination with further equalities between the power and cross-spectra, reduce the number of independent spectra to 13, a number reduced to seven if the power spectrum of the potential is assumed isotropic. The power-sum rules, cross-spectral phases, and coherence between components all provide information on the internal consistency of a set of gradiometry measurements. This information can be used to assess the noise, to determine the isotropy, and, for a self-similar source, to calculate the scaling factor and average depth. When applied to a data set collected in the North Sea, the power-sum rules reveal high-frequency noise that is distributed among only three of the gradient components; additionally, the coherences reveal the source to be anisotropic with a nonzero correlation length.
4
Kleeman, Richard. "Spectral Analysis of Multidimensional Stochastic Geophysical Models with an Application to Decadal ENSO Variability." Journal of the Atmospheric Sciences 68, no. 1 (2011): 13–25. http://dx.doi.org/10.1175/2010jas3546.1.
Full textAbstract:
Abstract Simple linear models with additive stochastic forcing have been rather successful in explaining the observed spectrum of important climate variables. Motivated by this, the authors analyze the spectral character of such a general stochastic system of finite dimension. The spectral matrix is derived in the case that the spectrum is a linear combination of dynamical variables and their stochastic forcings. It is found that the most convenient basis for analysis is provided by the normal modes. In general the spectrum consists of two pieces. The first “diagonal” piece is a symmetric Lorentzian curve centered on the normal mode frequencies with breadth and strength determined by the normal mode dissipation. The second cross-spectrum piece derives usually from the coherency of the stochastic forcing of two different normal modes. The cross-spectrum is smaller in magnitude than the corresponding two diagonal pieces. This relative magnitude is controlled by the Wiener coherency, which is equal to the magnitude of the correlation of the stochastic forcings of different normal modes. This new analysis framework is studied in detail for the ENSO case for which a two-dimensional stochastically forced oscillator has been previously suggested as a minimal model. It is found that the observed spectrum is rather easily reproduced given appropriate dissipation. Further, it is found that the cross-spectrum results in a phase-dependent enhancement or suppression of frequencies smaller than the dominant ENSO frequency. This therefore provides a new mechanism for decadal ENSO variability. Since the cross-spectrum is phase dependent, the decadal variability generated has a distinctive spatial character. The significance of the cross-spectrum depends on the Wiener coherency, which in turn depends on the statistics of the stochastic forcing.
5
Nuzhdina, M. A. "Connection between ENSO phenomena and solar and geomagnetic activity." Natural Hazards and Earth System Sciences 2, no. 1/2 (2002): 83–89. http://dx.doi.org/10.5194/nhess-2-83-2002.
Full textAbstract:
Abstract. Connections between El Niño – Southern Oscillation (ENSO) phenomena and indices of solar activity and geomagnetic disturbance were investigated. Spectral analysis of the ENSO-data was carried out. Oscillations with periods of about 11–12, 5–6, 2–3 years were found. Correlative and cross-spectral analysis was carried out to estimate connections between ENSO data, and solar and geomagnetic indices. Functions of coherency and phase were calculated.
6
Chen, Zhongbiao, Biao Zhang, Vladimir Kudryavtsev, Yijun He, and Xiaoqing Chu. "Estimation of Sea Surface Current from X-Band Marine Radar Images by Cross-Spectrum Analysis." Remote Sensing 11, no. 9 (2019): 1031. http://dx.doi.org/10.3390/rs11091031.
Full textAbstract:
The cross-spectral correlation approach has been used to estimate the wave spectrum from optical and radar images. This work aims to improve the cross-spectral approach to derive current velocity from the X-band marine radar image sequence, and evaluate the application conditions of the method. To reduce the dependency of gray levels on range and azimuth, radar images are preprocessed by the contrast-limited adaptive histogram equalization. Two-dimensional cross-spectral coherence and phase are derived from neighboring X-band marine radar images, and the phases with large coherences are used to estimate the phase velocity and angular frequency of waves, which are first fitted with the theoretical dispersion relation by different least square models, and then the current velocity can be determined. Compared with the current velocities measured by a current meter, the root-mean-square error, correlation coefficient, bias, and relative error are 0.15 m/s. 0.88, –0.05 m/s, and 7.79% for the north-south velocity, and 0.14 m/s, 0.86, 0.06 m/s, and 10.75% for the east-west velocity in the experimental area, respectively. The preprocessing, critical coherence, and the number of images for applying the cross-spectral approach, are discussed.
7
Privalsky, V. "On studying relations between time series in climatology." Earth System Dynamics 6, no. 1 (2015): 389–97. http://dx.doi.org/10.5194/esd-6-389-2015.
Full textAbstract:
Abstract. Relationships between time series are often studied on the basis of cross-correlation coefficients and regression equations. This approach is generally incorrect for time series, irrespective of the cross-correlation coefficient value, because relations between time series are frequency-dependent. Multivariate time series should be analyzed in both time and frequency domains, including fitting a parametric (preferably, autoregressive) stochastic difference equation to the time series and then calculating functions of frequency such as spectra and coherent spectra, coherences, and frequency response functions. The example with a bivariate time series "Atlantic Multidecadal Oscillation (AMO) – sea surface temperature in Niño area 3.4 (SST3.4)" proves that even when the cross correlation is low, the time series' components can be closely related to each other. A full time and frequency domain description of this bivariate time series is given. The AMO–SST3.4 time series is shown to form a closed-feedback loop system with a 2-year memory. The coherence between AMO and SST3.4 is statistically significant at intermediate frequencies where the coherent spectra amount up to 55 % of the total spectral densities. The gain factors are also described. Some recommendations are offered regarding time series analysis in climatology.
8
Chronis, Themis G., Earle Williams, and Emmanouil N. Anagnostou. "Evidence of Tropical Forcing of the 6.5-Day Wave from Lightning Observations over Africa." Journal of the Atmospheric Sciences 64, no. 10 (2007): 3717–21. http://dx.doi.org/10.1175/jas4021.1.
Full textAbstract:
Abstract A study employing observations and climatic reanalysis data is concerned with links between convection and the well-documented 6.5-day stratospheric global wave. Observations from a long-range lightning detection network, known as ZEUS, reveal an in-phase behavior between the maximization of daily lightning activity over Africa and the intensification of the wave. To extend the observations on a climatological basis, the authors make use of the outgoing longwave radiation (OLR) as proxy for convection and the surface level pressure (SLP) as an indicator of atmospheric column forcing. Cross-spectral analysis shows significant peaks in coherency between OLR and SLP, apparent only over equatorial Africa and South America (Amazon basin), while strong coherency in this frequency band is absent over the Maritime Continent.
9
Kriss, A. B., P. A. Paul, and L. V. Madden. "Variability in Fusarium Head Blight Epidemics in Relation to Global Climate Fluctuations as Represented by the El Niño-Southern Oscillation and Other Atmospheric Patterns." Phytopathology® 102, no. 1 (2012): 55–64. http://dx.doi.org/10.1094/phyto-04-11-0125.
Full textAbstract:
Cross-spectral analysis was used to characterize the relationship between climate variability, represented by atmospheric patterns, and annual fluctuations of Fusarium head blight (FHB) disease intensity in wheat. Time series investigated were the Oceanic Niño Index (ONI), which is a measure of the El Niño-Southern Oscillation (ENSO), the Pacific-North American (PNA) pattern and the North Atlantic Oscillation (NAO), which are known to have strong influences on the Northern Hemisphere climate, and FHB disease intensity observations in Ohio from 1965 to 2010 and in Indiana from 1973 to 2008. For each climate variable, mean climate index values for the boreal winter (December to February) and spring (March to May) were utilized. The spectral density of each time series and the (squared) coherency of each pair of FHB–climate-index series were estimated. Significance for coherency was determined by a nonparametric permutation procedure. Results showed that winter and spring ONI were significantly coherent with FHB in Ohio, with a period of about 5.1 years (as well as for some adjacent periods). The estimated phase-shift distribution indicated that there was a generally negative relation between the two series, with high values of FHB (an indication of a major epidemic) estimated to occur about 1 year following low values of ONI (indication of a La Niña); equivalently, low values of FHB were estimated to occur about 1 year after high values of ONI (El Niño). There was also limited evidence that winter ONI had significant coherency with FHB in Indiana. At periods between 2 and 7 years, the PNA and NAO indices were coherent with FHB in both Ohio and Indiana, although results for phase shift and period depended on the specific location, climate index, and time span used in calculating the climate index. Differences in results for Ohio and Indiana were expected because the FHB disease series for the two states were not similar. Results suggest that global climate indices and models could be used to identify potential years with high (or low) risk for FHB development, although the most accurate risk predictions will need to be customized for a region and will also require use of local weather data during key time periods for sporulation and infection by the fungal pathogen.
10
Zohar, Sioan, and Chun Hong Yoon. "Bi-cross validation of spectral clustering hyperparameters." Powder Diffraction 35, no. 2 (2020): 112–16. http://dx.doi.org/10.1017/s0885715620000214.
Full textAbstract:
One challenge impeding the analysis of terabyte scale X-ray scattering data from the Linac Coherent Light Source (LCLS) is determining the number of clusters required for the execution of traditional clustering algorithms. Here, we demonstrate that the previous work using bi-cross validation to determine the number of singular vectors directly maps to the spectral clustering problem of estimating both the number of clusters and hyperparameter values. Applying this method to LCLS X-ray scattering data enables the identification of dropped shots without manually setting boundaries on detector fluence and provides a path toward identifying rare and anomalous events.
Dissertations / Theses on the topic "Cross spectral coherency analysis"
1
Vowels, Matthew James. "THE APPLICATION OF SPECTRAL AND CROSS-SPECTRAL ANALYSIS TO SOCIAL SCIENCES DATA." UKnowledge, 2018. https://uknowledge.uky.edu/hes_etds/58.
Full textAbstract:
The primary goal of this paper is to demonstrate the application of a relatively esoteric and interdisciplinary technique, called spectral analysis, to dyadic social sciences data. Spectral analysis is an analytical and statistical technique, commonly used in engineering, that allows times series data to be analyzed for the presence of significant regular/periodic fluctuations/oscillations. These periodic fluctuations are reflected in the frequency domain as amplitude or energy peaks at certain frequencies. Furthermore, a Magnitude Squared Coherence analysis may be used to interrogate more than one time series concurrently in order to establish the degree of frequency domain correlation between the two series, as well to establish the phase (lead/lag) relationship between the coherent frequency components. In order to demonstrate the application of spectral analysis, the current study utilizes a secondary dyadic dataset comprising 30 daily reports of perceived sexual desire for 65 couples. The secondary goal of this paper is to establish a) whether there is significant periodic fluctuation in perceived levels of sexual desire for men and/or women, and at which specific frequencies, and b) how much correlation or `cross-spectral coherence' there is between partners' sexual desire within the dyads, and c) what the phase lead-lag relationship is between the partners at any of the identified frequency components. Sexual desire was found to have significant periodic components for both men and women, with a fluctuation of once per month being the most common frequency component across the groups of individuals under analysis. Mathematical models are presented in order to describe and illustrate these principal fluctuations. Partners in couples, on average, were found to fluctuate together at a number of identified frequencies, and the phase lead/lag relationships of these frequencies are presented.
2
Potočňák, Tomáš. "Klasifikace srdečních cyklů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-219953.
Full textAbstract:
The aim of this work was to develop the method for classification of ECG beats into two classes, namely ischemic and non-ischemic beats. Heart beats (P-QRS-T cycles) selected from animals orthogonal ECGs were preprocessed and used as the input signals. Spectral features vectors (values of cross spectral coherency), principal component and HRV parameters were derived from the beats. The beats were classified using feedforward multilayer neural network designed in Matlab. Classification performance reached the value approx. from 87,2 to 100%. Presented results can be suitable in future studies aimed at automatic classification of ECG.
3
Kanaan, Mona N. "Cross-spectral analysis for spatial point-lattice processes." Thesis, [n.p.], 2000. http://dart.open.ac.uk/abstracts/page.php?thesisid=94.
Full text
4
Kamboj, Sunita. "The cross-section for photoelectric-equivalent interactions in germanium for gamma-ray spectral analysis." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16633.
Full text
5
Spalt, Taylor Brooke. "Constrained Spectral Conditioning for the Spatial Mapping of Sound." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/70868.
Full textAbstract:
In aeroacoustic experiments of aircraft models and/or components, arrays of microphones are utilized to spatially isolate distinct sources and mitigate interfering noise which contaminates single-microphone measurements. Array measurements are still biased by interfering noise which is coherent over the spatial array aperture. When interfering noise is accounted for, existing algorithms which aim to both spatially isolate distinct sources and determine their individual levels as measured by the array are complex and require assumptions about the nature of the sound field.
This work develops a processing scheme which uses spatially-defined phase constraints to remove correlated, interfering noise at the single-channel level. This is achieved through a merger of Conditioned Spectral Analysis (CSA) and the Generalized Sidelobe Canceller (GSC). A cross-spectral, frequency-domain filter is created using the GSC methodology to edit the CSA formulation. The only constraint needed is the user-defined, relative phase difference between the channel being filtered and the reference channel used for filtering. This process, titled Constrained Spectral Conditioning (CSC), produces single-channel Fourier Transform estimates of signals which satisfy the user-defined phase differences. In a spatial sound field mapping context, CSC produces sub-datasets derived from the original which estimate the signal characteristics from distinct locations in space. Because single-channel Fourier Transforms are produced, CSC's outputs could theoretically be used as inputs to many existing algorithms. As an example, data-independent, frequency-domain beamforming (FDBF) using CSC's outputs is shown to exhibit finer spatial resolution and lower sidelobe levels than FDBF using the original, unmodified dataset. However, these improvements decrease with Signal-to-Noise Ratio (SNR), and CSC's quantitative accuracy is dependent upon accurate modeling of the sound propagation and inter-source coherence if multiple and/or distributed sources are measured.
In order to demonstrate systematic spatial sound mapping using CSC, it is embedded into the CLEAN algorithm which is then titled CLEAN-CSC. Simulated data analysis indicates that CLEAN-CSC is biased towards the mapping and energy allocation of relatively stronger sources in the field, which limits its ability to identify and estimate the level of relatively weaker sources. It is also shown that CLEAN-CSC underestimates the true integrated levels of sources in the field and exhibits higher-than-true peak source levels, and these effects increase and decrease respectively with increasing frequency. Five independent scaling methods are proposed for correcting the CLEAN-CSC total integrated output levels, each with their own assumptions about the sound field being measured. As the entire output map is scaled, these do not account for relative source level errors that may exist. Results from two airfoil tests conducted in NASA Langley's Quiet Flow Facility show that CLEAN-CSC exhibits less map noise than CLEAN yet more segmented spatial sound distributions and lower integrated source levels. However, using the same source propagation model that CLEAN assumes, the scaled CLEAN-CSC integrated source levels are brought into closer agreement with those obtained with CLEAN.<br>Ph. D.
6
Jaimes, Rafael. "Spatiotemporal Organization of Atrial Fibrillation Using Cross-Bicoherence with Surrogate Data." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/828.
Full textAbstract:
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.
7
Yeung, Wai. "Sleep, pain and daytime functioning in patients with fibromyalgia syndrome and osteoarthritis : a cross-sectional comparative study." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21798.
Full textAbstract:
Fibromyalgia syndrome (FMS) is a disorder characterised by chronic widespread pain, non-restorative sleep, fatigue and daytime dysfunction. Occurring in 2-5% of the population, the aetiology is largely unknown. Sleep dysfunction occurs in over 90% of FMS patients. While research has shown that both the macrostructure and microstructure of sleep may be altered, there remain inconsistencies in the polysomnographic (PSG) findings, and wide variations in methodological approaches. Few studies have controlled for symptom duration or the time elapsed between diagnosis and PSG sleep assessments. In addition, while psychometric analyses have suggested a distinctive FMS psychological profile (which includes higher levels of depressive symptoms, anxiety and fatigue) few studies have simultaneously, and thoroughly examined sleep and psychological status in the same participants. A frequently reported alteration found in the sleep microstructure of FMS patients is the alpha-delta sleep anomaly, characterised by an increase in alpha wave activity during slow wave sleep. Originally considered a possible neurological contribution to FMS, whether the alpha-delta sleep anomaly is fundamental to the development of fibromyalgia syndrome, or results mainly from the pain experience of FMS patients remains unknown. No previous study has directly compared the sleep of FMS and other (non-FMS) patients experiencing similar levels of chronic pain and sleep dysfunction. The present study was designed to examine sleep macrostructure and microstructure in FMS patients, and evaluate the role of the alpha-delta sleep anomaly as either a possible contributor to fibromyalgia syndrome, or a likely consequence of pain experience. In order to explore these relationships, detailed sleep, activity and psychological profiles were compared in 3 groups: 1) FMS patients (n = 19); 2) osteoarthritis patients with sleep disturbance (n = 17); and non-clinical (normal healthy) adults (n = 10). In order to standardise diagnostic reliability and symptom chronicity, the FMS group was recruited from a single rheumatology facility immediately following diagnosis. Guided by a series of formal research questions, analyses compared sleep macrostructure (using American Academy of Sleep Medicine criteria), sleep microstructure (using spectral analysis), and a range of psychological variables (including pain experience, sleepiness, fatigue, depression, anxiety, perceived social support, health locus of control, pain catastrophizing and personality). The results indicated that the alpha-delta sleep anomaly is not unique to FMS, but appears to be a feature found in the sleep of normal healthy adults and (to a greater extent) those with FMS and osteoarthritis. The incidence of the anomaly was statistically similar in both clinical (FMS and osteoarthritis) groups, a pattern consistent of its being a secondary feature of pain, rather than a primary abnormality of FMS. Overall, the psychometric assessments of state and trait anxiety and depression better discriminated between the three groups than did the sleep variables. Nevertheless, on measures of sleep, perceived social support, health locus of control, and pain catastrophizing, FMS and osteoarthritis patients were not significantly different, though both clinical groups differed on these variables from healthy controls.
8
Gavrilovic, Milan. "Spectral Image Processing with Applications in Biotechnology and Pathology." Doctoral thesis, Uppsala universitet, Centrum för bildanalys, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160574.
Full textAbstract:
Color theory was first formalized in the seventeenth century by Isaac Newton just a couple of decades after the first microscope was built. But it was not until the twentieth century that technological advances led to the integration of color theory, optical spectroscopy and light microscopy through spectral image processing. However, while the focus of image processing often concerns modeling of how images are perceived by humans, the goal of image processing in natural sciences and medicine is the objective analysis. This thesis is focused on color theory that promotes quantitative analysis rather than modeling how images are perceived by humans. Color and fluorescent dyes are routinely added to biological specimens visualizing features of interest. By applying spectral image processing to histopathology, subjectivity in diagnosis can be minimized, leading to a more objective basis for a course of treatment planning. Also, mathematical models for spectral image processing can be used in biotechnology research increasing accuracy and throughput, and decreasing bias. This thesis presents a model for spectral image formation that applies to both fluorescence and transmission light microscopy. The inverse model provides estimates of the relative concentration of each individual component in the observed mixture of dyes. Parameter estimation for the model is based on decoupling light intensity and spectral information. This novel spectral decomposition method consists of three steps: (1) photon and semiconductor noise modeling providing smoothing parameters, (2) image data transformation to a chromaticity plane removing intensity variation while maintaining chromaticity differences, and (3) a piecewise linear decomposition combining advantages of spectral angle mapping and linear decomposition yielding relative dye concentrations. The methods described herein were used for evaluation of molecular biology techniques as well as for quantification and interpretation of image-based measurements. Examples of successful applications comprise quantification of colocalization, autofluorescence removal, classification of multicolor rolling circle products, and color decomposition of histological images.
9
Kriss, Alissa Brynn. "The Role of Environmental, Temporal, and Spatial Scale on the Heterogeneity of Fusarium Head Blight of Wheat." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1320932280.
Full text
10
Milan, Juliana Cristina. "Estudo da sensibilidade barorreflexa e sua relação com a produção de citocinas inflamatórias no processo de envelhecimento." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/7037.
Full textAbstract:
Made available in DSpace on 2016-08-17T18:39:51Z (GMT). No. of bitstreams: 1
6222.pdf: 2879821 bytes, checksum: 010a3c6abf3b0c6f2ec81ebf9ff59ef0 (MD5)
Previous issue date: 2014-08-21<br>Universidade Federal de Sao Carlos<br>Aging causes changes in several human subsystems such as the cardiovascular and immune systems. The objective of this study was to evaluate the relationship between baroreflex function through linear algorithm (cross-spectral analysis) and proinflammatory cytokines in the aging process and also assess the baroreflex sensitivity, TNF-α, IL-6 and hsCRP in different ages and in the aging process. One hundred and ten apparently healthy subjects divided into 5 groups with 22 individuals each, according to age were evaluated: 21-30 years, 30-40 years, 40-50 years, 50-60 years, 60-70 years. The experimental protocol consisted of a blood samples collection for analysis of inflammatory markers and in the same day were collected ECG, blood pressure and respiratory movements for 15 minutes in the supine position and in standing position, after the active postural change for 15 minutes. For the analysis of baroreflex sensitivity cross spectral analysis (coherence, phase and gain) was used and ELISA method for analysis of TNF-α and IL-6 was used. Data were analyzed using analysis of variance one-way ANOVA test with Tukey test post-hoc or Kruskal-Wallis oneway ANOVA with Dunn's post-hoc according to the normality of the data and the Spearman correlation test. The level of significance for the tests was 5%. The main results were: 1) reduced baroreflex sensitivity during the aging process; 2) increased levels of inflammatory markers in the aging process; 3) negative correlation between IL-6 and BF gain and phase; 4) negative relationship between hsCRP and coherence, phase and gain in BF. It can be concluded that the human natural aging causes a loss of baroreflex sensitivity and increased serum levels of inflammatory markers studied, although the decrease in baroreflex sensitivity as function of the decreasing of vagal autonomic function occurred in the 41-50 age range, and only in the next age was observed changes in inflammatory markers.<br>O envelhecimento causa alterações em diversos subsistemas humanos como o cardiovascular e imunológico. O objetivo deste trabalho foi avaliar a relação entre a função barorreflexa, por meio de algoritmo linear (análise espectral cruzada) e citocinas próinflamatórias no processo de envelhecimento e ainda, avaliar a sensibilidade barorreflexa, IL- 6, TNF-α e PCRus em diversas faixas etárias e no processo de envelhecimento. Foram avaliados 110 indivíduos aparentemente saudáveis divididos em 5 grupos com 22 indivíduos cada, de acordo com a faixa etária: 21-30 anos, 30-40 anos, 40-50 anos, 50-60 anos, 60-70 anos. O protocolo experimental consistiu em uma coleta de amostras de sangue para a análise dos marcadores inflamatórios e no mesmo dia foram coletados o eletrocardiograma (ECG), a pressão arterial de pulso e a respiração por 15 minutos na postura supina, logo após foi realizada a mudança postural ativa de supino para ortostatismo, permanecendo 15 minutos nesta posição a coleta de sangue. Para a análise da sensibilidade barorreflexa foi utilizada a analise espectral cruzada e o método ELISA para análise das citocinas TNF-α e IL-6. Os dados foram analisados por meio do teste de análise de variância ANOVA one-way com posthoc de Tukey ou Kruskal-Wallis ANOVA one-way com post-hoc de Dunn s de acordo com a normalidade dos dados e teste de Correlação de Spearman. O nível de significância estabelecido para os testes foi de 5%. Os principais resultados foram: 1) redução da sensibilidade barorreflexa durante o processo de envelhecimento; 2) aumento dos níveis dos marcadores inflamatórios no processo de envelhecimento; 3) relação negativa entre a IL-6 e fase e ganho em BF; 4) relação negativa entre PCRus e coerência, fase e ganho em BF. Podese concluir que o envelhecimento natural humano causa a redução da sensibilidade barorreflexa e aumento dos níveis séricos dos marcadores inflamatórios estudados, ainda a diminuição da sensibilidade barorreflexa em consequência da diminuição da função autonômica vagal correu na faixa etária 41-50 e somente na faixa etária seguinte foi observada alterações nos marcadores inflamatórios.
Books on the topic "Cross spectral coherency analysis"
1
Pakko, Michael R. A spectral analysis of the cross-country consumption correlation puzzle. Federal Reserve Bank of St. Louis, 2003.
Find full text
2
Pittaras, N. Spectral and cross-spectral analysis of unequally spaced time series with applications to astronomical data. UMIST, 1995.
Find full text
3
Buchinsky, Moshe. Leads and lags in commodity prices: An application of cross-spectral analysis. World Bank, 1987.
Find full text
4
Bieler, Heribert. Theoretische Untersuchungen uber primare Instabilitaten in dreidimensionalen Grenzschichtstromungen. DFVLR, 1986.
Find full text
5
King, Wayne M. Multitaper spectral estimation and time-domain cross-correlation in FMRI data analysis: Actual and simulated data. 1999.
Find full textBook chapters on the topic "Cross spectral coherency analysis"
1
Zhuang, Yuming, and Degang Chen. "Algorithms for Accurate Spectral Analysis in the Presence of Arbitrary Non-coherency and Large Distortion." In Accurate and Robust Spectral Testing with Relaxed Instrumentation Requirements. Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-77718-4_2.
Full text
2
Bull, Günther. "Sodar investigations of gravity waves by cross spectral analysis." In Acoustic Remote Sensing Applications. Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/bfb0009570.
Full text
3
Přibil, Jiří, and Anna Přibilová. "Spectral Flatness Analysis for Emotional Speech Synthesis and Transformation." In Cross-Modal Analysis of Speech, Gestures, Gaze and Facial Expressions. Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03320-9_11.
Full text
4
Johnson, Rodney W., and John E. Shore. "Introduction to Minimum-Cross-Entropy Spectral Analysis of Multiple Signals." In Maximum-Entropy and Bayesian Methods in Inverse Problems. Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-017-2221-6_3.
Full text
5
Cury, Claire, Marco Lorenzi, David Cash, et al. "Spatio-Temporal Shape Analysis of Cross-Sectional Data for Detection of Early Changes in Neurodegenerative Disease." In Spectral and Shape Analysis in Medical Imaging. Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-51237-2_6.
Full text
6
Xie, Yumeng, Peilin Zhang, and Yong Wang. "Inland Waterborne Commerce Study Based on Variance Decomposition and Cross-Spectral Analysis." In Advances in Artificial Systems for Logistics Engineering. Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-80475-6_2.
Full text
7
Erla, S., C. Papadelis, L. Faes, C. Braun, and G. Nollo. "Studying Brain Visuo-Tactile Integration through Cross-Spectral Analysis of Human MEG Recordings." In XII Mediterranean Conference on Medical and Biological Engineering and Computing 2010. Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-13039-7_19.
Full text
8
Lenk, Ulrich, Kurt Seitz, and Bernhard Heck. "A Datum Defect and Spectral Analysis in Regional Cross-Over Adjustments of Satellite Altimeter Data." In International Association of Geodesy Symposia. Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-79721-7_36.
Full text
9
Hashimoto, Kengo. "Subcriticality." In Accelerator-Driven System at Kyoto University Critical Assembly. Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-0344-0_2.
Full textAbstract:
AbstractFor a subcritical reactor system driven by a periodically pulsed spallation neutron source in KUCA, the Feynman-α and the Rossi-α neutron correlation analyses are conducted to determine the prompt neutron decay constant and quantitatively to confirm a non-Poisson character of the neutron source. The decay constant determined from the present Feynman-α analysis well agrees with that from a previous analysis for the same subcritical system driven by an inherent source. Considering the effect of a higher mode excited, the disagreement can be successfully resolved. The power spectral analysis on frequency domain is also carried out. Not only the cross-power but also the auto-power spectral density have a considerable correlated component even at a deeply subcritical state, where no correlated component could be previously observed under a 14 MeV neutron source. The indicator of the non-Poisson character of the present spallation source can be obtained from the spectral analysis and is consistent with that from the Rossi-α analysis. An experimental technique based on an accelerator-beam trip or restart operation is proposed to determine the subcritical reactivity of ADS. Applying the least-squares inverse kinetics method to the data analysis, the subcriticality can be inferred from time-sequence neutron count data after these operations.
10
"Minimum Cross Entropy Spectral Analysis." In Entropy Theory and its Application in Environmental and Water Engineering. John Wiley & Sons, Ltd, 2013. http://dx.doi.org/10.1002/9781118428306.ch12.
Full textConference papers on the topic "Cross spectral coherency analysis"
1
Hall, Andre´ M., Mark N. Glauser, and Charles E. Tinney. "An Experimental Investigation of the Pressure-Velocity Cross-Correlation in an Axisymmetric Jet." In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77338.
Full textAbstract:
This study investigates the strength of the pressure-velocity correlations of a Mach 0.6, axisymmetric jet, with an exit nozzle diameter of 50.8mm. Experiments are conducted at a constant exit temperature of 25°C, and exit pressure and temperature are balanced with ambient conditions. The instantaneous velocity measurements are acquired using a multi-component LDA system who’s measurement volume is traversed along several radial and streamwise locations within the potential core, and mixing layer regions of the flow. The fluctuating lip pressure is simultaneously sampled by an azimuthal array of (15) dynamic transducers, evenly spaced at 24°. These are positioned just outside the shear layer near the jet exit at z/D = 0.875, and 1.75R from the centerline, where the pressure field has been shown to be hydrodynamic. From this multi-point evaluation, the cross-correlations between the near-field pressure array (fixed), and streamwise component of the velocity field (traversed) are examined as a function of radial, streamwise, and also azimuthal separation. The results illustrate a remarkable coherence between the near field pressure and the velocity field, on the order of 25%. Streamwise convection velocities of 0.77Uj and 0.73Uj are calculated within the potential core and shear layer, respectively. Analysis of the coherency spectra illustrates the frequency band of the correlations and suggest that the potential core and mixing layer regions of the flow are, in general, governed by the high and low frequency motions of the flow, respectively. The azimuthal modal distribution of the cross-correlation shows the dominance of the column mode of the jet, with no higher modes exhibited within the potential core region, and only modes 1 & 2 within the shear layer.
2
Pessoa, Joa˜o, Nuno Fonseca, Suresh Rajendran, and C. Guedes Soares. "Experimental Investigation of the First and Second Order Wave Exciting Forces on a Restrained Body in Long Crested Irregular Waves." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-50318.
Full textAbstract:
The paper presents an experimental investigation of the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is restrained from moving. Second order spectral analysis is applied to obtain the linear spectra, coherence spectra and cross bi-spectra of both the incident wave elevation and of the horizontal and vertical wave exciting forces. Then the linear and quadratic transfer functions (QTF) of the exciting forces are obtained. The QTF obtained from the analysis of irregular wave measurements are compared with results from experiments in bi-chromatic waves and with numerical predictions from a second order potential flow code.
3
Chiocchini, S., T. Pagliaroli, R. Camussi, and E. Giacomazzi. "A Mutual Nearest Neighbours Based Chaotic Synchronization Index to Detect Thermo-Acoustic Coupling in Gas Turbine Combustion Instabilities." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56222.
Full textAbstract:
The characterization of unstable combustion regimes is often performed in the light of the Rayleigh Criterion, in the frequency domain, employing the Power Spectral Analysis of pressure (p′) and heat-release (q′) fluctuations. Equally often, it is assumed a priori that the thermo-acoustic oscillations are periodic, with a dominant frequency and a fixed amplitude (Period-1Llimit Cycle Oscillations). However one has to consider that: 1) p′ and q′, involved in the Rayleigh instability index, are governed by the Linearized Acoustic Energy Perturbation Balance Equations; 2) in the frequency domain any interdependence is measured by the coherence function, based on cross spectral densities, or Fourier spectra of cross-correlations, that in turn suppose a linear interdependence between sampled quantities. Conversely, recent experiments reveal that even simple thermo-acoustic systems exhibit nonlinear behaviour, far more elaborate than period-1 limit cycle oscillations. Therefore, in addition to the conventional linear analysis, a new approach based on Nonlinear Dynamics will be required to characterize the unstable regimes in lean gas-turbine combustors. With such approach, one may avoid the risk of misunderstanding the Deterministic Chaos, underlying in the measured signals also during stable combustion regimes, as stochastic noise. The preserved information will be thus available to analytically formulate an index acting as the earliest warning signal of an impending oscillatory combustion instability. In the light of this, we have applied the Interdependence Index E, based on chaotic synchronization theory, to pressure and radiant energy signals sampled from an industrial combustor. The index was found: 1) low computationally demanding, since based on quantities already calculated for the phase space reconstruction; 2) really effective in the early detection of self sustained (chaotic or not) thermo-acoustic oscillations; 3) valid for a range of coupling strength, and thus smoothly increasing at the instability onset, as requested by the control system time response; 4) unaffected by the non linear relationship between heat release an chemiluminescence, that may make invalid the pseudo-Rayleigh index, computed from pressure and radiant energy fluctuations; 5) asymmetric and thus able to identify the driven and driver (sub)systems, as in combustion instabilities with no thermo-acoustic feed-back.
4
Hamakawa, Hiromitsu, Yuji Kouno, and Eiichi Nishida. "Effect of Fins on Vortex Shedding Noise Generated From a Circular Cylinder in Cross Flow." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30290.
Full textAbstract:
In the present paper, the effect of twist-serrated fins around a bare tube on the Aeolian tone was experimentally investigated. These fins were mounted spirally around a bare tube and had the same geometry as those actually used in boiler tubes. We measured the intensity of velocity fluctuation, spectrum of velocity fluctuation, coherence of Karman vortex in the spanwise direction, dynamic lift force, and sound pressure level of the aerodynamic noise generated from finned tubes with various fin pitches. An Aeolian tone induced by Karman vortex shedding was observed in the case of a finned tube, although the complicated fin was mounted around a bare tube. A decrease in the pitch of the fin effectively caused an increase in the equivalent diameter, which acted as the characteristic length of a cylinder with fins. The equivalent diameter depended on the Reynolds number. We modified a relation to calculate the characteristic diameter of the finned tube, which in turn was used to calculate the Strouhal number. The coherent scales in the spanwise direction for the cases with various fin pitches were slightly larger than that of a simple circular cylinder. It is known that the sound pressure level of the Aeolian tone depends on the coherent scale of the Karman vortex in the spanwise direction. However, when the pitch of the fins decreased, the peak level of the sound pressure spectrum decreased. A correlation analysis between the flow field and Aeolian tone was carried out.
5
Merzari, Elia, Paul Fischer, and Justin Walker. "Large-Scale Simulation of Rod Bundles: Coherent Structure Recognition and Stability Analysis." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-29719.
Full textAbstract:
The axial flow in rod bundles has been the object of several investigations, since they are relevant for various industrial applications (e.g., heat exchangers, nuclear reactor cores). For tight configurations (pitch-to-diameter ratio smaller than 1.1) the large difference in velocity within the cross section creates the possibility of a Kelvin-Helmholtz instability and the generation of a vortex street in the gap (“gap instability”). While the presence of spacing devices may perturb the flow, simple grid spacers — grids of the type usually encountered in sodium fast reactors — do not prevent this instability. This work seeks to improve our understanding of the gap instability in large rod bundles by using high-fidelity large-eddy simulation (LES). The application of LES methods has been historically limited to single-pin calculations because of the large cost of full-bundle calculations. However, using Nek5000, a massively parallel spectral-element computational fluid dynamics code, we are able to carry out well-resolved LES simulations for this class of geometries. Results are compared with experimental data. For the largest bundle case, over 8 billion collocation points at a polynomial order of 20 are judged necessary to achieve overall excellent accuracy. More than 500,000 processors are used to carry out the simulations (costing approximately 50,000,000 CPU-hours), and 3,000 snapshots of the flow field have been collected to apply several coherent structure recognition techniques, including one of the largest proper orthogonal decompositions carried out to date. Also investigated here is the effect of geometry, including the (presence of spacers, changing pitch-to-diameter ratio, and canister wall. In particular, global linear stability analysis is applied to a series of simplified geometries in order to gain insight into the physics of the gap instability.
6
Hermle, Georg, and Martin Lawerenz. "Unsteady Secondary Flow in an Annular Compressor Cascade." In ASME 2013 Gas Turbine India Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gtindia2013-3560.
Full textAbstract:
Subject of the experimental investigations presented is the analysis of secondary flow in an annular compressor cascade. Focus lies on the so-called rotating instability. The investigations concentrate on the unsteady pressure field in the area of the blade tip clearance in order to get deeper understanding of the phenomenon of rotating instability. Therefore, transducers were mounted along the leading edges around the circumference of the cascade. This arrangement allows the determination of the coherence and the phasing between the transducers by the cross correlation via Fourier and wavelet transform. The results show the influence of the Mach number and the incidence angle on the onset of the phenomenon. Furthermore, a relation between the characteristic frequencies of the rotating instability to certain modal types can be stated. Moreover, the wavelet cross power spectrum suggests that the phenomenon is not continuously present within the spectra but shows an unsteady appearance.
7
Pavesi, Giorgio, Guido Ardizzon, and Giovanna Cavazzini. "Unsteady Flow Field and Noise Generation in a Centrifugal Pump Impeller With a Vaneless Diffuser." In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77320.
Full textAbstract:
To improve understanding of the phenomena of stall in centrifugal pumps, extensive research was conducted to investigate the impact on flow field instabilities and the noise generated in a pump equipped with a diffuser. A pump fitted with a vaneless diffuser and a return channel was used as the test model. Flow velocity was measured at the pump and at diffuser inflow to establish a link between the flow field structure and acoustic radiation. Activity was based upon the cross spectral analysis of output signals from piezoelectric transducers placed flush with the wall at the inflow and outflow of the pump, and 3D fully-viscous unsteady computations. Results showed the jet-wake flow pattern induced an unstable vortex, which influenced flow discharging from the adjacent passage and destabilised jet-wake flow in the passage. Consequently, periodic fluctuations were seen at impeller discharge which were found to be coherent from blade to blade and possessed a rich harmonic content. With the exception of the total pressure in the far field, the pressure frequency scattering by the pump was found to be consistent when compared to the experimental and analytic results.
8
Jusserand, Franc¸ois, Andre´ Adobes та Tseheno N. Randrianarivelo. "Solving U-RANS k-ω SST Equations and Post-Processing Motion Independent Fluid Forces in a Tube Bundle". У ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77691.
Full textAbstract:
The computation of the dynamic response of a structure subjected to a fluid flow requires the knowledge of the fluid forces acting on the structure. At least three classes of these forces can be distinguished: - fluid-elastic forces due to the coupling between fluid flow and structure displacement; - random forces due to the turbulent nature of the flow. In cases of two-phase fluid configurations, such as those occurring in steam generators of nuclear power plants, forces due to the two-phase nature of the fluid are also assumed to be part of this type of excitations; - fluid forces due to coherent structures in the flow, such as Von Karman vortex-streets downstream of a single tube in cross-flow. In this paper we focus on the numerical study of this last class of excitations. We propose here a method to compute the dimensionless spectrum of those forces as a function of a scaled parameter called “reduced frequency” [1]. We perform CFD (Computational Fluid Dynamics) calculations with the EDF (Electricite´ De France) CFD software Code_Saturne® [2], using a U-RANS (Unsteady-Reynolds Averaged Navier Stokes) approach, and a k-ω SST (Shear Stress Transport) model. Tube wall fluid stresses are derived and post-processed into spectra. This numerical methodology allows one to distinguish the drag from the lift component in overall fluid force. The paper includes three parts: - In the first part, the numerical method of our study is presented: the k-ω SST model developed to solve U-RANS equations [2] is described. We then detail the post-processing used to compute the dimensionless spectrum starting from fluid stresses at tube walls. - In the second part, k-ω SST model’s implementation is validated on the case of a single rigid tube in an upwards cross-flow of water. CFD results are compared to experimental measurements [3]. - Eventually the study of a 2D rigid tube bundle subjected to a two-phase cross-flow modeled by an equivalent single phase flow is presented. A sensitivity analysis is carried out to study the influence of bundle’s bulk and the Reynolds number. Wall pressures are post-processed to derive the dimensionless spectrum associated with fluid forces due to coherent structures.
9
Stockwell, Robert G., Robert P. Lowe, and L. Mansinha. "Localized cross-spectral analysis with phase-corrected wavelets." In Aerospace/Defense Sensing and Controls, edited by Harold H. Szu. SPIE, 1996. http://dx.doi.org/10.1117/12.236027.
Full text
10
Jadhav, Pankaj, Debabrata Datta, and Siddhartha Mukhopadhyay. "Signature Matching For Seismic Signal Identification." In International Conference on Women Researchers in Electronics and Computing. AIJR Publisher, 2021. http://dx.doi.org/10.21467/proceedings.114.17.
Full textAbstract:
Seismic signals can be classified as natural or manmade by matching signature of similar events that have occurred in the past. Waveform matching techniques can be effectively used for discrimination since the events with similar location and focal mechanism have similar waveform irrespective of magnitude. The seismic signals are inherently non-stationary in nature. The analysis of such signals can be best achieved in multiresolution framework by resolving the signal using continuous wavelet transform (CWT) in time-frequency plane. In this paper similarity testing and classification of nuclear explosion and earthquake are exploited with correlation, continuous wavelet transform, cross-wavelet transform and wavelet coherence (WC) of P phase of seismogram. Clustering of seismic signals continuous wavelet spectra is performed using maximum covariance analysis. The proposed classifier has an average classification accuracy of 94%.
Reports on the topic "Cross spectral coherency analysis"
1
Pakko, Michael R. A Spectral Analysis of the Cross-Country Consumption Correlation Puzzle. Federal Reserve Bank of St. Louis, 2003. http://dx.doi.org/10.20955/wp.2003.023.
Full text