Search results for "frequency analysi"

A Linear Cost Algorithm to Compute the Discrete Gabor Transform

2010

In this paper, we propose an alternative efficient method to calculate the Gabor coefficients of a signal given a synthesis window with a support of size much lesser than the length of the signal. The algorithm uses the canonical dual of the window (which does not need to be calculated beforehand) and achieves a computational cost that is linear with the signal length in both analysis and synthesis. This is done by exploiting the block structure of the matrices and using an ad hoc Cholesky decomposition of the Gabor frame matrix.

Salikteņu lietojums korporatīvās atbildības ziņojumos

2018

Šī pētījuma mērķis ir noskaidrot, kāda salikteņu forma un funkcija ir visbiežāk izmantota korporatīvās atbildības ziņojumos. Analīzei tika izvēlēti trīs korporatīvās atbildības ziņojumi banku nozarē. Izmantotā empīriskā pētījuma metode bija biežuma analīze, un analīze tika balstīta uz Bauera (1983), Levija (1998) un Liebera (2009) teorijām. Pētījuma rezultāti liecina, ka katram analizētajam korporatīvās atbildības ziņojumam ir sava visbiežāk lietotā salikteņu forma. Visvairāk lietotais saliktenis visos analizētajos korporatīvās atbildības ziņojumos ir salikts lietvārds, un vismazāk lietoti ir saliktie darbības vārdi un apstākļa vārdi. Analīze arī parāda, ka lielākā salikteņu daļa ir saistīt…

Uncertainty evaluation of design rainfall for urban flood risk analysis

2011

A reliable and long dataset describing urban flood locations, volumes and depths would be an ideal prerequisite for assessing flood frequency distributions. However, data are often piecemeal and long-term hydraulic modelling is often adopted to estimate floods from historical rainfall series. Long-term modelling approaches are time- and resource-consuming, and synthetically designed rainfalls are often used to estimate flood frequencies. The present paper aimsto assess the uncertainty of such an approach and for suggesting improvements in thedefinition of synthetic rainfall data for flooding frequency analysis. According to this aim, a multivariate statistical analysis based on a copulameth…

Inclusion of Instantaneous Influences in the Spectral Decomposition of Causality: Application to the Control Mechanisms of Heart Rate Variability

2021

Heart rate variability is the result of several physiological regulation mechanisms, including cardiovascular and cardiorespiratory interactions. Since instantaneous influences occurring within the same cardiac beat are commonplace in this regulation, their inclusion is mandatory to get a realistic model of physiological causal interactions. Here we exploit a recently proposed framework for the spectral decomposition of causal influences between autoregressive processes [2] and generalize it by introducing instantaneous couplings in the vector autoregressive model (VAR). We show the effectiveness of the proposed approach on a toy model, and on real data consisting of heart period (RR), syst…

Concatenated trial based Hilbert-Huang transformation on event-related potentials

2010

Time-frequency analysis is critical to study event-related potentials (ERPs) now. ERPs are usually generated through averaging over a number of trials, and such averaging limits the application of a nonlinear time-frequency analysis method—Hilbert-Huang transformation (HHT). This is because HHT usually requires very long recordings to sufficiently decompose the complicated signal into oscillations and the averaged ERP trace tends to possess only hundreds of samples. Thus, this study designs the concatenated trial based HHT to release the limitation on the decomposition. Such a paradigm may reveal better temporal and spectral properties of an ERP than the conventional wavelet transformation …

Vection lies in the brain of the beholder: EEG parameters as an objective measurement of vection

2015

Analysis of the level-crossing rate and average duration of fades of WSSUS channels

2017

Studies of the level-crossing rate (LCR) and the average duration of fades (ADF) are so far only devoted to stochastic processes being a function of one independent variable, which is usually time or in some few cases frequency. In this paper, we study the LCR (ADF) of wide-sense stationary uncorrelated scattering (WSSUS) processes in the time-frequency domain. A closed-form solution will be derived for the so-called time-frequency LCR (ADF) of the absolute value of the time-variant transfer function (TVTF) of WSSUS processes. It is shown that the LCR (ADF) is circularly symmetric in the normalized time-frequency domain. The derived time-frequency LCR contains the time LCR and frequency LCR…

Analysis on the Time and Frequency Domains of the Acceleration in Front Crawl Stroke

2012

Analysis on the Time and Frequency Domains of the Acceleration in Front Crawl Stroke The swimming involves accelerations and decelerations in the swimmer's body. Thus, the main objective of this study is to make a temporal and frequency analysis of the acceleration in front crawl swimming, regarding the gender and the performance. The sample was composed by 31 male swimmers (15 of high-level and 16 of low-level) and 20 female swimmers (11 of high-level and 9 of low-level). The acceleration was registered from the third complete cycle during eight seconds in a 25 meters maximum velocity test. A position transducer (200Hz) was used to collect the data, and it was synchronized to an aquatic ca…

Epoch Parameterization by Gabor Atom Density in Experimental Epilepsy

2007

An Electrocorticogram (ECoG), during an epilepsy episode can change dramatically from the normal state into a high amplitude low frequency signal and suddenly return to the normal sate. It is possible to identify some stages in the epilepsy seizure, the most representative of them: basal, preictal, ictal and posictal. ECoG are highly non periodical signals, so they are analyze with T-F algorithms, in order to follow up its frequency evolution through the seizure stages. Each seizure stage has different frequency components and they show up at different time. Experimental epilepsy produce by kindling model in rats is used; signals are recorded at cortex level. The ECoG is decompose by means …

The Wigner Distribution of Sum-of-Cissoids and Sum-of-Chirps Processes for the Modelling of Stationary and Non-Stationary Mobile Channels

2016

This paper concerns the time-frequency analysis of stationary and non-stationary multipath flat fading channels. For the modelling of stationary multipath fading channels, we use a sum-of-cisoids (SOCi) process, while the non-stationary channel is modelled by a sum-of-chirps (SOCh) process that captures the time-variant Doppler effect caused by speed variations of the mobile station. For the time-frequency analysis, we apply the concept of the Wigner distribution. Closed-form solutions are provided for the Wigner distribution of SOCi and SOCh processes. It is shown that the obtained Wigner distributions can be expressed by the sum of an auto-term representing the true Doppler power spectral…