scholarly journals Some results of analysis of inverted echo-sounder records from the Atlantic equatorial region

1985 ◽  
Vol 33 (2) ◽  
pp. 213-218
Author(s):  
Alberto dos Santos Franco ◽  
Joseph Harari ◽  
Afrânio Rubens de Mesquita
Keyword(s):  
Spectral Analysis ◽  
Internal Waves ◽  
Frequency Band ◽  
Equatorial Region ◽  
Temperature Series ◽  
The Other ◽  
Tidal Analysis ◽  
Frequency Bands ◽  
Inverted Echo Sounder ◽  
Even Harmonics

The tidal analysis of data from the Equatorial region, given by inverted echo-sounders, show considerable residuals in the frequency band of approximately 2 cycles per day. In the even harmonics of 4 and 6 cycles per day, tidal components statistically not negligible are also identified. Spectral analysis of temperature series from the same area show, on the other hand, variabilities in the same frequency bands, which suggests the occurrence of internal waves with energy distributed in these frequency bands, in the Atlantic Equatorial area.

scholarly journals EEG Power Spectral Analysis of Abnormal Cortical Activations During REM/NREM Sleep in Obstructive Sleep Apnea

2021 ◽  
Vol 12 ◽  
Author(s):  
Shuling Liu ◽  
Jiucheng Shen ◽  
Yezhou Li ◽  
Jing Wang ◽  
Jianhua Wang ◽  
...  
Keyword(s):  
Obstructive Sleep Apnea ◽  
Spectral Analysis ◽  
Power Spectral Analysis ◽  
Nrem Sleep ◽  
The Other ◽  
Frequency Bands ◽  
Delta Band ◽  
Power Spectral ◽  
Obstructive Sleep ◽  
Eeg Power

Objective: To characterize electroencephalogram (EEG) power in different frequency bands during rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep in patients with obstructive sleep apnea (OSA).Methods: Retrospective data on 151 patients were collected and divided into three groups: primary snoring group (AHI < 5/h), mild-moderate OSA group (6 ≤ AHI < 30/h), and severe OSA group (AHI ≥ 30/h). EEG recordings in the frontal, central, and occipital regions were extracted from both REM and NREM sleep, to compute the normalized spectral power densities in the delta, theta, alpha, sigma, beta, and gamma frequency bands, using Fast Fourier Transform. Correlations between the computed EEG power and PSG parameters were analyzed.Results: In NREM sleep, elevated normalized power spectral density (PSD) in the delta band was observed in the severe OSA group compared to the other two groups. In contrast, the PSD of the other frequency bands showed a corresponding decrease in the severe OSA group. In REM sleep, similar changes were observed in the frontal region. Delta band PSD was positively correlated with Apnea Hypopnea Index (AHI) (r = 0.33), longest time of apnea, oxygen desaturation index (ODI) (r = 0.34), percent sleep time below 90% SaO2 (T90%) (r = 0.30), Arousal Index (ArI) (r = 0.29), and negatively correlated with N3%, minimum oxygen saturation (minSaO2).Conclusion: Our findings provide neurophysiological evidence for pathological cortical activation during REM/NREM sleep, which may be associated with the arousals and cognitive impairments in OSA. The technique of power spectral analysis could prove a potentially useful tool in complementing traditional PSG parameters in assessing disease burden to guide therapeutic decisions.

Comparison of various techniques used to estimate spontaneous baroreflex sensitivity (the EuroBaVar study)

2004 ◽  
Vol 286 (1) ◽  
pp. R226-R231 ◽  
Author(s):  
Dominique Laude ◽  
Jean-Luc Elghozi ◽  
Arlette Girard ◽  
Elisabeth Bellard ◽  
Malika Bouhaddi ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Frequency Band ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
The Other ◽  
Data Sets ◽  
Noninvasive Blood Pressure ◽  
Sequence Method ◽  
Baroreflex Failure ◽  
Spontaneous Baroreflex

This study compared spontaneous baroreflex sensitivity (BRS) estimates obtained from an identical set of data by 11 European centers using different methods and procedures. Noninvasive blood pressure (BP) and ECG recordings were obtained in 21 subjects, including 2 subjects with established baroreflex failure. Twenty-one estimates of BRS were obtained by methods including the two main techniques of BRS estimates, i.e., the spectral analysis (11 procedures) and the sequence method (7 procedures) but also one trigonometric regressive spectral analysis method (TRS), one exogenous model with autoregressive input method (X-AR), and one Z method. With subjects in a supine position, BRS estimates obtained with calculations of α-coefficient or gain of the transfer function in both the low-frequency band or high-frequency band, TRS, and sequence methods gave strongly related results. Conversely, weighted gain, X-AR, and Z exhibited lower agreement with all the other techniques. In addition, the use of mean BP instead of systolic BP in the sequence method decreased the relationships with the other estimates. Some procedures were unable to provide results when BRS estimates were expected to be very low in data sets (in patients with established baroreflex failure). The failure to provide BRS values was due to setting of algorithmic parameters too strictly. The discrepancies between procedures show that the choice of parameters and data handling should be considered before BRS estimation. These data are available on the web site ( http://www.cbi.polimi.it/glossary/eurobavar.html ) to allow the comparison of new techniques with this set of results.

scholarly journals Temporal Loudness Weights Are Frequency Specific

2021 ◽  
Vol 12 ◽  
Author(s):  
Alexander Fischenich ◽  
Jan Hots ◽  
Jesko Verhey ◽  
Daniel Oberfeld
Keyword(s):  
Frequency Band ◽  
Band 3 ◽  
Primacy Effect ◽  
The Other ◽  
Second Sound ◽  
Frequency Bands ◽  
Lower Frequency Band

Previous work showed that the beginning of a sound is more important for the perception of loudness than later parts. When a short silent gap of sufficient duration is inserted into a sound, this primacy effect reoccurs in the second sound part after the gap. The present study investigates whether this temporal weighting occurs independently for different frequency bands. Sounds consisting of two bandpass noises were presented in four different conditions: (1) a simultaneous gap in both bands, (2) a gap in only the lower frequency band, (3) a gap in only the higher frequency band, or (4) no gap. In all conditions, the temporal loudness weights showed a primacy effect at sound onset. For the frequency bands without a gap, the temporal weights decreased gradually across time, regardless of whether the other frequency band did or did not contain a gap. When a frequency band contained a gap, the weight at the onset of this band after the gap was increased. This reoccurrence of the primacy effect following the gap was again largely independent of whether or not the other band contained a gap. Thus, the results indicate that the temporal loudness weights are frequency specific.

scholarly journals Spillovers of Stock Markets among the BRICS: New Evidence in Time and Frequency Domains before the Outbreak of COVID-19 Pandemic

2021 ◽  
Vol 14 (3) ◽  
pp. 112
Author(s):  
Kai Shi
Keyword(s):  
Stock Market ◽  
Frequency Band ◽  
Stock Markets ◽  
Emerging Market ◽  
Low Frequency ◽  
Systematic Risk ◽  
Error Variance ◽  
Frequency Bands ◽  
Volatility Spillovers ◽  
Risk Sources

We attempted to comprehensively decode the connectedness among the abbreviation of five emerging market countries (BRICS) stock markets between 1 August 2002 and 31 December 2019 not only in time domain but also in frequency domain. A continuously varying spillover index based on forecasting error variance decomposition within a generalized abbreviation of vector-autoregression (VAR) framework was computed. With the help of spectral representation, heterogeneous frequency responses to shocks were separated into frequency-specific spillovers in five different frequency bands to reveal differentiated linkages among BRICS markets. Rolling sample analyses were introduced to allow for multiple changes during the sample period. It is found that return spillovers dominated by the high frequency band (within 1 week) part declined with the drop of frequencies, while volatility spillovers dominated by the low frequency band (above 1 quarter) part grew with the decline in frequencies; the dynamics of spillovers were influenced by crucial systematic risk events, and some similarities implied in the spillover dynamics in different frequency bands were found. From the perspective of identifying systematic risk sources, China’s stock market and Russia’s stock market, respectively, played an influential role for return spillover and volatility spillover across BRICS markets.

Quantitative acoustic emission investigation on the crack evolution in concrete prisms by frequency analysis based on wavelet packet transform

2021 ◽  
pp. 147592172110188
Author(s):  
Zonglian Wang ◽  
Keqin Ding ◽  
Huilan Ren ◽  
Jianguo Ning
Keyword(s):  
Acoustic Emission ◽  
Frequency Band ◽  
Wavelet Packet ◽  
Strain Energy Release ◽  
Crack Size ◽  
Frequency Bands ◽  
Emission Signal ◽  
Damage Process ◽  
Concrete Materials ◽  
Stage 1

To gain an insight into the evolution of micro-cracks in concrete materials, a quantitative acoustic emission investigation on the damage process of concrete prisms subjected to three-point bending loading was performed. Each of the monitored acoustic emission signals was processed by a two-level wavelet packet decomposition into four different frequency bands (AA2, DA2, AD2, and DD2), and the energy coefficients R1, R2, R3, and R4 that parameterize their characteristic frequency bands were calculated. By analyzing variations in energy coefficients of the lowest frequency band (AA2), R1, and the energy coefficients of the highest frequency band (DD2), R4, the whole damage process was divided into three stages: crack initiation, crack growth, and crack coalescence. An inverse relationship between the frequency of the acoustic emission signal emitted by the propagating crack and the crack size in concrete materials was acquired based on the damage theory of brittle materials and the strain energy release theory. The statistical analysis results of the experimental data indicated that the average of R1 increased in turn, and the average of R4 correspondingly decreased in turn from Stage 1 to Stage 3. It revealed that the frequencies of acoustic emission signals decreased gradually with the evolution of the damage of concrete prisms, which is in a good agreement with the theoretical analysis result.

An Effective Brain Imaging Biomarker for AD and aMCI: ALFF in Slow-5 Frequency Band

2021 ◽  
Vol 18 ◽  
Author(s):  
Luoyu Wang ◽  
Qi Feng ◽  
Mei Wang ◽  
Tingting Zhu ◽  
Enyan Yu ◽  
...  
Keyword(s):  
Brain Imaging ◽  
Frequency Band ◽  
Low Frequency ◽  
Posterior Cingulate Cortex ◽  
Angular Gyrus ◽  
Imaging Biomarker ◽  
Support Vector ◽  
Frequency Bands ◽  
Local Functional ◽  
Left Angular Gyrus

Background: As a potential brain imaging biomarker, amplitude of low frequency fluc-tuation (ALFF) has been used as a feature to distinguish patients with Alzheimer’s disease (AD) and amnestic mild cognitive impairment (aMCI) from normal controls (NC). However, it remains unclear whether the frequency-dependent pattern of ALFF alterations can effectively distinguish the different phases of the disease. Methods: In the present study, 52 AD and 50 aMCI patients were enrolled together with 43 NC in total. The ALFF values were calculated in the following three frequency bands: classical (0.01-0.08 Hz), slow-4 (0.027-0.073 Hz) and slow-5 (0.01-0.027 Hz) for the three different groups. Subsequently, the local functional abnormalities were employed as features to examine the effect of classification among AD, aMCI and NC using a support vector machine (SVM). Results: We found that the among-group differences of ALFF in the different frequency bands were mainly located in the left hippocampus (HP), right HP, bilateral posterior cingulate cortex (PCC) and bilateral precuneus (PCu), left angular gyrus (AG) and left medial prefrontal cortex (mPFC). When the local functional abnormalities were employed as features, we identified that the ALFF in the slow-5 frequency band showed the highest accuracy to distinguish among the three groups. Conclusion: These findings may deepen our understanding of the pathogenesis of AD and suggest that slow-5 frequency band may be helpful to explore the pathogenesis and distinguish the phases of this disease.

scholarly journals Diurnal mesospheric tidal winds observed simultaneously by meteor radar in Costa Rica (10° N, 86° W) and Cariri (7° S, 37° W)

2019 ◽  
Author(s):  
Ricardo A. Buriti ◽  
Wayne Hocking ◽  
Paulo P. Batista ◽  
Igo Paulino ◽  
Ana R. Paulino ◽  
...  
Keyword(s):  
Costa Rica ◽  
Geographical Location ◽  
Equatorial Region ◽  
The Other ◽  
Meteor Radar ◽  
Santa Cruz ◽  
Poor Agreement ◽  
Vertical Wavelength ◽  
Local Climate ◽  
Different Response

Abstract. This paper is about a study of diurnal tides on meteor wind observed simultaneously by two meteor radars sited on equatorial region. The radar are located in Santa Cruz (10.3° N, 85.6° W), Costa Rica (hereafter CR) and in São João do Cariri (7.4° S, 36.5° W), Brazil (hereafter CA). The distance between them is 5800 km. Harmonic analysis was used to get information of amplitude and phase (hour of peak amplitude) of diurnal, semidiurnal and terdiurnal tides between 82 and 98 km of height. The period of observation was from April 2005 to January 2006. The results were compared to GSWM00 model. In general, seasonal agreement between observation and model was satisfactory to zonal and meridional amplitudes. Values of zonal and meridional amplitudes from November to January to CR were very different of GSWM00. Peak of zonal amplitude (~ 25 m/s) to CR was observed in September and December between 90 and 94 km. On the other hand, meridional phase was excellent to both sites and vertical wavelength of 25 km was observed practically every month to CR and CA. The zonal phase presented some difficult to get vertical wavelength according to criteria adopted to calculate it. Considering diurnal zonal amplitude, when we compare CR and CA, we could expect a poor agreement of amplitude between them. That is normal if we believe that this is because the geographical location of both sites are completely different in terms of local climate even if they are close to the equator and effect of heat latent release could lead to different response at high altitudes.

scholarly journals An Improved Method for Discerning Broken Rotor Bar Fault and Load Oscillation in Induction Motors

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3130 ◽  
Author(s):  
Liling Sun ◽  
Boqiang Xu
Keyword(s):  
Spectral Analysis ◽  
Theoretical Basis ◽  
Induction Motors ◽  
The Other ◽  
Improved Method ◽  
Broken Rotor Bar ◽  
Signal Parameters ◽  
Analysis Technique ◽  
Novel Strategy ◽  
The One

A few methods for discerning broken rotor bar (BRB) fault and load oscillation in induction motors have been reported in the literature. However, they all perhaps inevitably fail in adverse cases in which these two phenomena are simultaneously present. To tackle this problem, an improved method for discerning BRB fault and load oscillation is proposed in this paper based on the following work. On the one hand, the theoretical basis is analytically extended to include such an adverse case, yielding some important findings on the spectra of the instantaneous reactive and active powers. A novel strategy is thus outlined to correctly discern BRB fault and load oscillation even when simultaneously present. On the other hand, Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT) is adopted as the spectral analysis technique to deal with the instantaneous reactive and active powers, yielding a certain improvement compared to the existing methods, adopting Fast Fourier Transform (FFT). Simulation and experimental results demonstrate that the proposed method can correctly discern BRB fault and load oscillation even when simultaneously present.

scholarly journals Cloud Changes in the Period of Global Warming: the Results of the International Satellite Project

2019 ◽  
pp. 3-13
Author(s):  
O. M. Pokrovsky
Keyword(s):  
Temperature Series ◽  
The Other ◽  
Coefficient Of Determination ◽  
Smoothing Algorithm ◽  
Temperature Changes ◽  
Lower Cloud ◽  
Statistical Time ◽  
The One ◽  
The Tropics ◽  
Climatic Series

The results of analysis of climatic series of global and regional cloudiness for 1983–2009. Data were obtained in the framework of the international satellite project ISCCP. The technology of statistical time series analysis including smoothing algorithm and wavelet analysis is described. Both methods are intended for the analysis of non-stationary series. The results of the analysis show that both global and regional cloudiness show a decrease of 2–6%. The greatest decrease is observed in the tropics and over the oceans. Over land, the decrease is minimal. The correlation coefficient between the global cloud series on the one hand and the global air and ocean surface temperature series on the other hand reaches values (–0.84) — (–0.86). The coefficient of determination that characterizes the accuracy of the regression for the prediction of global temperature changes based on data on changes in the lower cloud, in this case is 0.316.

scholarly journals Changes in Degree Centrality of Network Nodes in Different Frequency Bands in Parkinson’s Disease With Depression and Without Depression

2021 ◽  
Vol 15 ◽  
Author(s):  
Haiyan Liao ◽  
Jinyao Yi ◽  
Sainan Cai ◽  
Qin Shen ◽  
Qinru Liu ◽  
...  
Keyword(s):  
Basal Ganglia ◽  
Magnetic Resonance ◽  
Frequency Band ◽  
Limbic System ◽  
Resting State ◽  
Brain Regions ◽  
Degree Centrality ◽  
Functional Magnetic Resonance ◽  
Frequency Bands ◽  
Medial Frontal Gyrus

BackgroundDepression induces an early onset of Parkinson’s disease (PD), aggravates dyskinesia and cognitive impairment, and accelerates disease progression. However, it is very difficult to identify and diagnose PD with depression (PDD) in the early clinical stage. Few studies have suggested that the changes in neural networks are associated with PDD, while degree centrality (DC) has been documented to be effective in detecting brain network changes.ObjectivesThe objectives of this study are to explore DC changes between patients with PDD and without depression (PDND) and to find the key brain hubs involved with depression in PD patients.MethodsOne hundred and four PD patients and 54 healthy controls (HCs) underwent brain resting-state functional magnetic resonance imaging. The Data Processing and Analysis of Brain Imaging and Resting-State Functional Magnetic Resonance Data Analysis Toolkit were used for processing and statistical analysis. The DC value of each frequency band was calculated. One-way analysis of variance and a two-sample t-test for post hoc comparison were used to compare the differences of the DC values in different frequency bands among PDD, PDND, and healthy control group. Gaussian random field was used for multiple comparison correction. Pearson correlation analysis was performed between each individual’s DC map and clinical indicators.ResultsThe DC value of different brain regions changed in PDD and PDND in different frequency bands. The prefrontal lobe, limbic system, and basal ganglia were the main brain regions involved. PDD patients showed a wider range and more abnormal brain areas in the slow-4 frequency band (0.027–0.073 Hz) compared to the HCs. PDD showed a decreased DC value in the medial frontal gyrus, bilateral cuneus gyrus, right lingual gyrus, bilateral supplementary motor area (SMA), bilateral superior frontal gyrus, and left paracentral lobule, but an increased DC value in the bilateral brainstem, midbrain, bilateral parahippocampal gyrus, cerebellum, left superior temporal gyrus, bilateral insula, left fusiform gyrus, and left caudate nucleus in the traditional frequency band (0.01–0.08 Hz) compared to PDND patients. PDND patients displayed more abnormal functions in the basal ganglia in the slow-4 frequency band.ConclusionThe DC changes in PDD and PDND are frequency dependent and frequency specific. The medial frontal gyrus, SMA, and limbic system may be the key hubs for depression in PD.

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