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1
Content available remote Trend and nonstationary relation of extreme rainfall: Central Anatolia, Turkey
Oruc Sertac
Acta Geophysica
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2021
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Vol. 69, no. 1
243--255
EN
The frequency of extreme rainfall occurrence is expected to increase in the future and neglecting these changes will result in the underestimation of extreme events. Nonstationary extreme value modelling is one of the ways to incorporate changing conditions into analyses. Although the defnition of nonstationary is still debated, the existence of nonstationarity is determined by the presence of signifcant monotonic upward or downward trends and/or shifts in the mean or variance. On the other hand, trend tests may not be a sign of nonstationarity and a lack of signifcant trend cannot be accepted as time series being stationary. Thus, this study investigated the relation between trend and nonstationarity for 5, 10, 15, and 30 min and 1, 3, 6, and 24 h annual maximum rainfall series at 13 stations in Central Anatolia, Turkey. Trend tests such as Mann– Kendall (MK), Cox–Stuart (CS), and Pettitt’s (P) tests were applied and nonstationary generalized extreme value models were generated. MK test and CS test results showed that 33% and 27% of 104 time series indicate a signifcant trend (with p<0.01–p<0.05–p<0.1 signifcance level), respectively. Moreover, 43% of time series have outperformed nonstationary (NST) models that used time as covariate. Among fve diferent time-variant nonstationary models, the model with a location parameter as a linear function of time and the model with a location and scale parameter as a linear function of time performed better. Considering the rainfall series with a signifcant trend, increasing trend power may increase how well fitted nonstationary models are. However, it is not necessary to have a signifcant trend to obtain outperforming nonstationary models. This study supported that it is not necessarily time series to have a trend to perform better nonstationary models and acceptance of nonstationarity solely depending on the presence of trend may be misleading.
2
Content available remote Adaptive classification to reduce non-stationarity in visual evoked potential brain-computer interfaces
Kapgate Deepak, Kalbande Dhananjay, Shrawankar Urmila
Bio-Algorithms and Med-Systems
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2019
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Vol. 15, no. 2
art. no. 20190020
EN
Non-stationarity of electroencephalogram (EEG) signals greatly affect classifier performance in brain-computer interface (BCI). To overcome this problem we propose an adaptive classifier model known as extended multiclass pooled mean linear discriminant analysis (EMPMLDA). Here, we update the average class pair co-variance matrix along with pooled mean values. Evaluation of classifiers are done on visual evoked cortical potential data-sets. We demonstrate that EMPMLDA can significantly outperform other static classifiers such as MLDA and adaptive classifiers (MPMLDA). Furthermore an optimal update coefficient can be achieved using different datasets.
3
Content available remote Improved Gabor Deconvolution and Its Extended Applications
Sun X., Sun S. Z.
Acta Geophysica
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2016
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Vol. 64, no. 1
61--75
EN
In log time-frequency spectra, the nonstationary convolution model is a linear equation and thus we improved the Gabor deconvolution by employing a log hyperbolic smoothing scheme which can be implemented as an iteration process. Numerical tests and practical applications demonstrate that improved Gabor deconvolution can further broaden frequency bandwidth with less computational expenses than the ordinary method. Moreover, we attempt to enlarge this method’s application value by addressing nonstationary and evaluating Q values. In fact, energy relationship of each hyperbolic bin (i.e., attenuation curve) can be taken as a quantitative indicator in balancing nonstationarity and conditioning seismic traces to the assumption of unchanging wavelet, which resultantly reveals more useful information for constrained reflectivity inversion. Meanwhile, a statistical method on Q-value estimation is also proposed by utilizing this linear model’s gradient. In practice, not only estimations well agree with geologic settings, but also applications on Q-compensation migration are favorable in characterizing deep geologic structures, such as the pinch-out boundary and water channel.
4
Content available remote Heart rate variability assessment with rational-dilation wavelet transform
Buchner T., Grzyb G., Krzesiński P.
Bio-Algorithms and Med-Systems
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2013
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Vol. 9, no. 1
29--35
EN
Wavelet transform on a rational dilation is proposed as a method of assessment of spectral power in low and high frequency (LF and HF, respectively) bands for heart rate variability (HRV) analysis. One of the unique properties of this method is a possibility to align the band limits of certain scales with the limits of ranges LF and HF used in HRV analysis. The method parameters are optimized for use in the context of HRV analysis. Suitable examples are tilt test recordings analyzed using the optimized rational-dilation wavelet transform method.
5
Content available Verification of Doppler effect removal method for the needs of pass-by railway condition monitoring system
Dybała J., Gałęzia A., Mączak J.
Diagnostyka
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2008
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nr 4(48)
5-8
EN
The description of the experiment verifying the method of Doppler's Effect removal from the acoustic signal of moving object was discussed in the paper. Doppler's Effect was removed by dynamic resampling according to the theoretical frequency changes curve as well as with use of the curve obtained by passband filtration of the signal around the carrier frequency and differentiation of the phase of the analytic signal. Described solutions were tested in the GPS synchronised field measurements on the moving railway cars and simultaneously the stationary measurements taken next to the railway track.
PL
W pracy przedstawiono opis eksperymentu weryfikującego metodę usuwanie efektu Dopplera z sygnału akustycznego poruszającego się obiektu. Efekt Dopplera z sygnału usuwano poprzez dynamiczne przepróbowanie sygnału zarówno zgodnie z teoretyczną krzywą zmian częstotliwości chwilowej sygnału jak również z użyciem krzywej otrzymanej przez wąskopasmową filtrację sygnału wokół częstotliwości nośnej a następnie różniczkowanie fazy sygnału analitycznego. Zaproponowane rozwiązania zostały przetestowane w warunkach poligonowych podczas jednoczesnych, synchronizowanych sygnałem GPS, pomiarów na poruszających się pociągach oraz pomiarów przytorowych.
6
Content available Use of task-oriented dynamic resampling in reduction of signal non-stationarity
Dybała J.
Diagnostyka
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2008
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nr 4(48)
25-30
EN
The article presents method of reducing the non-stationarity of a signal which relies on task - oriented dynamic signal resampling. The characteristic feature of this method is lack of preliminary assumptions regarding the phenomenon causing the eliminated non-stationarity. Thanks to this the method enables not only elimination of the non-stationarity caused by linear change of the frequency of signal but also other complex and non-linear forms of non- stationarity. The paper also includes the examples of application of the described method.
PL
W artykule przedstawiono metodę redukcji niestacjonarności sygnału bazującą na zorientowanym zadaniowo dynamicznym przepróbkowaniu sygnału. Charakterystyczną cechą metody jest brak wstępnych założeń co do zjawiska wywołującego eliminowaną niestacjonarność. Dzięki temu metoda pozwala na usunięcie nie tylko niestacjonarności wywołanej liniową zmianą częstotliwości sygnału ale także i innych, złożonych i nieliniowych form niestacjonarności. W pracy zamieszczono także przykłady zastosowania opisanej metody.
7
Statistical control of process with autocorrelated data.
Koch J., Koch T., Dziuba R.
Postępy Technologii Maszyn i Urządzeń
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1998
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vol. 22, nr 4
95-106
EN
In the paper problem of statistical control of process, which do not meet data independence assumption, were described. It concerns both stationary and wandering processes. Data autocorrelation impact on control chart properties was analysed using process simulation. Results of the analysis were used to develop the guidelines for applying control charts for processes with autocorrelated data.
PL
Opisano problem statystycznego sterowania procesem, w przypadku którego nie jest spełniony warunek dotyczący niezależności danych. Opisany zakres badań zawiera zarówno procesy charakteryzujące się stacjonarnością, jak i takie, w których występuje dryf. Szczegółowa analiza wpływu autokorelacji na właściwości karty kontrolnej została oparta na badaniach symulacyjnych. Uzyskane wyniki wykorzystano do opracowania algorytmu stosowania kart kontrolnych w celu nadzorowania procesów charakteryzujących się autokorelacją danych.
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