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1
Content available remote Stator current spectrum analysis applied on short-circuit fault diagnosis of SRM
EN
Thanks to power electronics innovation, switched reluctance machine are taking place on industrial applications. In this paper we present the short-circuit fault diagnosis between stator turns of the switched reluctance machine by the use of stator current spectral analysis. To do this, we modeled our switched reluctance machine by permeance networks method to which we have associated the of the teeth contour permeance for the calculation of the airgap. The simulation results show the interest and efficiency of the proposed model as well as the stator current spectral analysis technique for the short circuit fault diagnosis of the switched reluctance machine.
PL
W artykule zaprezentowano metodę wykrywania zwarć w silniku reluktancyjnym. Metoda ta bazuje na analizie widmowej prądu stojana.
EN
Position time series from permanent Global Navigation Satellite System (GNSS) stations are commonly used for estimating secular velocities of discrete points on the Earth’s surface. An understanding of background noise in the GNSS position time series is essential to obtain realistic estimates of velocity uncertainties. The current study focuses on the investigation of background noise in position time series obtained from thirteen permanent GNSS stations located in Nepal Himalaya using the spectral analysis method. The power spectrum of the GNSS position time series has been estimated using the Lomb–Scargle method. The iterative nonlinear Levenberg–Marquardt (LM) algorithm has been applied to estimate the spectral index of the power spectrum. The power spectrum can be described by white noise in the high frequency zone and power law noise in the lower frequency zone. The mean and the standard deviation of the estimated spectral indices are […] for north, east and vertical components, respectively. On average, the power law noise extends up to a period of ca. 21 days. For a shorter period, i.e. less than ca. 21 days, the spectra are white. The spectral index corresponding to random walk noise (ca. –2) is obtained for a site located above the base of a seismogenic zone which can be due to the combined effect of tectonic and nontectonic factors rather than a spurious monumental motion. Overall, the usefulness of investigating the background noise in the GNSS position time series is discussed.
EN
In the presented study multi-year time series of changes in the L1 pseudo-range multipath are analysed. Data from 8 stations of the EUREF Permanent Network (EPN) were used in the study. Periodic components present in the signal and their stability over time were analysed. Also, the type of background noise was determined, based on the spectral index. In some cases, the presence of weak components with a 1/2 and 1/3 of the Chandler period has also been found. Time-frequency analysis shows that periodic signals are not stationary in most of the examined cases, and particular signal components occur only temporarily. The analysed signals were char-acterised by pink noise in the lower frequency range and by white noise for higher frequencies, which is also characteristic for time series of coordinates obtained from GNSS measurements.
PL
Zaletami metody HR CS MAS są wysoka czułość, niskie granice wykrywalności, szeroki zakres liniowości oraz ograniczenie przygotowania próbki di minimum, a także odporność na interferencje. Z tego powodu można przypuszczać, że wysokorozdzielcza absorpcyjna spektrometria cząsteczkowa z ciągłym źródłem promieniowania może stać się coraz powszechniej stosowaną techniką oznaczania fluoru w laboratoriach analitycznych.
PL
Elektroencefalografia jest techniką powszechnie stosowaną w diagnostyce medycznej oraz w badaniach. W artykule opisano zasadę pomiarów EEG i scharakteryzowano aparaturę pomiarową oraz metody rejestracji. Artykuł podzielony jest na dwie części. W pierwszej przedstawiono metody rejestracji sygnałów EEG oraz ich zastosowania kliniczne, a w drugiej narzędzia analizy widmowej. W pracy zostały użyte rzeczywiste sekwencje sygnałów EEG określone przez lekarza jako sygnały prawidłowe oraz wskazujące na chorobę (napadowe). Ich analiza została wykonana za pomocą szybkiej transformaty Fouriera oraz dyskretnej transformaty falkowej. Obliczano widmo mocy, a uzyskane średnie wartości mocy spektralnej stanowiły podstawę wskazania stanu patologicznego.
EN
Electroencephalography, as an electrophysiological method to record electrical activity of the brain, is commonly used in medicine and research areas. This article presents theoretical basics of EEG measurement. This method is still being developed. The greatest emphasis is put on improvement of the measuring equipment and recording methods. The solutions to improve hardware and software are still sought. This article is divided into two main parts. The first part explains EEG recording and its clinical applications. Epilepsy is the most common neurological disorder. The future trends in the development of EEG are pointed out. In the second part spectral analysis tools are presented. The EEG signal has nonlinear and nonstationary properties In the paper, real EEG sequences described by a doctor as normal and epileptic (ictal) are used. The analysis is performed using fast Fourier transform and discrete wavelet transform. The power spectrum in each frequency band is calculated. The obtained average power spectral values allow to distinguish epileptic sequences. Spectral analysis is considered to be a potential tool that may aid in the diagnosis of neurological diseases.
EN
The presence of deposits on heat exchange surfaces in condensers and regenerative exchangers of ship and land steam power plants is always connected with the increase of the wall temperature on the water vapor side due to additional thermal resistances resulting from accumulated deposits. This increase always results in an increase in the condensing pressure, which results in the deterioration of the condensation process of the water vapor, leading to thermal degradation of a given heat exchanger. In addition, the resulting deposits form unevenness with a diversified, often stochastic, geometric structure of the surface layer surface, whose measure is most often the roughness parameters, describing the geometric structure of the surface. In addition, the increase in surface roughness of the heat transfer surface on the water vapor side promotes the formation of a thicker layer of condensate, thus worsening the organization of condensate runoff, which results in interference of the thermal degradation phenomenon of a given heat exchange apparatus. As a result, these phenomena lead to a reduction in the efficiency of a given thermal system, and thus entail an increase in the costs of energy conversion and consequently cause an increased degradation of the natural environment. In the article, based on the results of the author’s own experimental research, the types of pollution accumulating on heat exchange surfaces on the water vapor side of heat exchange apparatus in marine and land steam power plants and quantitative measures of the unevenness of the surface layer of these sediments are presented.
EN
In this study, the temperature influence on the spectral responsivity of a Light Emitting Diode (LED) used as a photoreceptor, combined to light source spectrum is correlated to electrical characteristics in order to propose an alternative method to estimate LED junction temperature, regardless of the absolute illumination intensity and based on the direct correlation between the integral of the product of two optical spectra and the photo-generated currents. A laboratory test bench for experimental optical measurements has been set in order to enable any characterizing of photoelectric devices in terms of spectral behaviour, in a wavelength range placed between 400–1000 nm, and of current-voltage characteristics as function of temperature by using two different illumination sources. The temperature is analysed in a range from 5°C up to 85°C, so as to evaluate thermal variation effects on the sensor performance. The photo-generated current of two LEDs with different peak wavelengths has been studied. Research has observed and mathematically analysed what follows: since the photo-generated current strictly depends on the combination between the spectral response of the photoreceptor and the lighting source response, it becomes possible to estimate indirectly the junction temperature of the LEDs by considering the ratio between the photogenerated currents obtained by using two different illumination sources. Such results may for one thing increase knowledge in the fields where LEDs are used as photo-detectors for many applications and for another, they could be extended to generic photodetectors, thus providing useful information in photovoltaic field, for instance.
9
Content available remote Polarization of the longitudinal Pochhammer-Chree waves
EN
The exact solutions of the linear Pochhammer-Chree equation for propagating harmonicwaves in a cylindrical rod, are analyzed. Spectral analysis of the matrix dispersionequation for longitudinal axially symmetric modes is performed. Analytical expressionsfor displacement fields are obtained. Variation of wave polarization on the free surfacedue to variation of Poisson's ratio and circular frequency is analyzed. It is observed thatat the phase speed coinciding with the bulk shear wave speed all the components of thedisplacement eld vanish, meaning that no longitudinal axisymmetric Pochhammer-Chree wave can propagate at this phase speed.
PL
Azotowanie jarzeniowe tytanu i jego stopów jest jedną z obróbek powierzchniowych umożliwiających wytworzenie warstw o wysokich twardościach. Celem pracy było dokonanie analizy porównawczej składu jakościowego widma procesowego uzyskanego na tytanowym ekranie aktywnym, z widmem wzorcowym w rurkach spektralnych. Plazmę procesową tworzyły gazy Ar, N2, H2 wprowadzane w przestrzeń wylądowania jarzeniowego. Analizowano widmo spektralne w trzech etapach technologii azotowania jarzeniowego tytanu którymi były: przygotowanie komory próżniowej i oprzyrządowania do procesu, aktywacja powierzchni tytanu w wyładowaniu jarzeniowym, azotowanie jarzeniowe tytanu. Przedstawiono badania oceny wpływu temperatury azotowania jarzeniowego na zmianę sygnału spektralnego plazmy H2, N2, Ar oraz analizowano oddziaływanie zmiany proporcji reaktywnych gazów H2, N2 na sygnał spektralny plazmy. Badania te doprowadziły do próby zdefiniowania nowego parametru sterującego składem mieszanki gazowej wprowadzanej w obszar wyładowania jarzeniowego. Do realizacji celów pracy wykorzystano analizator spektralny plazmy oraz stanowisko badawcze — komorę próżniową pozwalającą naprowadzenie procesu azotowania jarzeniowego na potencjale katody, plazmy oraz potencjale uzupełniającym.
EN
The glow discharge nitriding of titanium and its alloys is one of the surface treatments enabling the formation of high hardness layers. The aim of the paper was to perform a comparative analysis of the qualitative composition of the process spectrum obtained on the titanium active screen with the reference spectrum in the spectral tubes. The process plasma was formed by the gases: Ar, N2 H2 introduced into the glow discharge space. The spectral spectrum was analyzed in three stages of the technology of glow discharge nitriding of titanium, which were: preparation of the vacuum chamber and process instrumentation, activation of the titanium surface in glow discharge, glow discharge nitriding of titanium. The paper presents the studies on the evaluation of the influence of the glow discharge nitriding temperature on the change in the plasma spectral signal H2,N2, Ar and analyzes the influence of the change in the proportions of reactive gases H2,N2 on the spectral signal of the plasma. These studies led to an attempt to define a new parameter controlling the composition of the gas mixture introduced into the glow discharge area. To achieve the goals of the paper, a plasma spectral analyzer and a test stand were used - a vacuum chamber allowing the glow discharge nitriding process to be carried out at the cathode, plasma and complementary potential.
EN
The article is devoted to the problem of voice signals recognition means introduction in the system of distance learning. The results of the conducted research determine the prospects of neural network means of phoneme recognition. It is also shown that the main difficulties of creation of the neural network model, intended for recognition of phonemes in the system of distance learning, are connected with the uncertain duration of a phoneme-like element. Due to this reason for recognition of phonemes, it is impossible to use the most effective type of neural network model on the basis of a multilayered perceptron, at which the number of input parameters is a fixed value. To mitigate this shortcoming, the procedure, allowing to transform the non-stationary digitized voice signal to the fixed quantity of mel-cepstral coefficients, which are the basis for calculation of input parameters of the neural network model, is developed. In contrast to the known ones, the possibility of linear scaling of phoneme-like elements is available in the procedure. The number of computer experiments confirmed expediency of the fact that the use of the offered coding procedure of input parameters provides the acceptable accuracy of neural network recognition of phonemes under near-natural conditions of the distance learning system. Moreover, the prospects of further research in the field of development of neural network means of phoneme recognition of a voice signal in the system of distance learning is connected with an increase in admissible noise level. Besides, the adaptation of the offered procedure to various natural languages, as well as to other applied tasks, for instance, a problem of biometric authentication in the banking sector, is also of great interest.
PL
Celem artykułu jest przedstawienie wyników analizy czasowo-częstotliwościowej sygnałów fonokardiograficznych. Powodem podjęcia działań dotyczących badania tego typu sygnałów są statystyki Światowej Organizacji Zdrowia, które od lat wskazują, iż pierwszą przyczyną zgonów na świecie są choroby układu sercowo-naczyniowego [1]. Powodem dominacji tego typu schorzeń w statystykach jest rosnący stres psychospołeczny oraz malejąca aktywność fizyczna społeczeństwa. Badanie tonów serca i detekcja schorzeń w oparciu o sygnał fonokardiograficzny na wczesnym etapie badań lekarskich może skutecznie przyczynić się do zmniejszenia wysokich statystyk umieralności. W artykule przedstawiono wyniki opracowanego algorytmu, który dla 15 osobowego zbioru przypadków charakteryzuje się czułością na poziomie 100% i specyficznością równą 87,50%, co z medycznego punktu widzenia jest wynikiem satysfakcjonującym.
EN
The aim of this article is to present the results of time-frequency analysis of phonocardiographic signals. The reason for undertaking such studies is the World Health Organization (WHO) statistics, which for years have shown that cardiovascular disease is the leading cause of death in the world [1]. The reason for the dominance of this type of illness in statistics is the increasing psychosocial stress and decreasing physical activity of the population. Heart rate and disease detection based on phonocardiographic data at an early stage of medical examination can effectively contribute to the reduction of high mortality statistics. The paper presents the results of the developed algorithm, which for the 15-person case collection is characterized by a sensitivity of 100% and a specificity of 87.50%, which is a satisfactory result from the medical point of view.
PL
Zakres zastosowań metody obserwacji magnetycznego szumu Barkhausena (BN) do nieniszczącego badania stanu lub właściwości materiałów magnetycznych stale rośnie. Z uwagi na stochastyczną naturę efektu Barkhausena niezbędne staje się użycie zaawansowanych metod analizy w celu ilościowej oceny obserwowanych zależności. Wiele czynników może wpływać na różne właściwości sygnałów BN wyrażanych w dziedzinie czasu i częstotliwości. Dlatego też obserwacja zmian dynamiki tego zjawiska wymaga analizy obu reprezentacji podczas procesu ekstrakcji cech. Z tego powodu korzystne staje się stosowanie metod transformacji czasowo-częstotliwościowych (tf) sygnałów. W tym artykule, w celu połączenia informacji dostarczonych w czasie i częstotliwości, zastosowano krótkoczasową transformatę Fouriera (ST FT). Przeprowadzono analizę uzyskanych reprezentacji tf sygnałów BN otrzymanych dla próbek stalowych o różnym stopniu zniszczenia i przedstawiono wyniki.
EN
The scope of applications of the magnetic Barkhausen noise observation (BN) method for non-destructive testing of the state or properties of magnetic materials is constantly increasing. Due to the stochastic nature of the Barkhausen effect, it is necessary to use advanced methods of analysis in order to quantify the observed relationships. Many factors can affect the various properties of BN signals expressed in the domain of time and frequency. Therefore, observation of changes in the dynamics of this phenomenon requires the analysis of both representations during the process of extraction of features. For this reason, it is preferable to use methods for transforming signals into time-frequency (tf) representation. In this article, a Short-Time Fourier Transform (ST FT) was used to combine information provided in time and frequency. The analysis of tf representations of BN signals obtained for steel samples representing various degrees of damage was performed and the results were presented.
EN
Azimuthally averaged power spectra are widely used in the Curie point depth (CPD) estimation with the implicit assumption that the magnetization distribution is random and uncorrelated. However, the marine magnetic anomalies are caused by bands of normal and reverse magnetization and show obvious trends. To investigate the effects of the anisotropy of marine magnetic anomalies on the CPD estimates, we develop 3D fractal striped magnetization models to produce lineated marine magnetic anomalies for the first time. We analyze the spectra anisotropy of the lineated magnetic anomalies of the synthetic fractal striped magnetization models and investigate its effects on the CPD estimates. The synthetic models and actual data show that the spectra of the lineated marine magnetic anomalies are directionally anisotropic. The amplitude response is strong and the slope of the logarithmic spectrum is large in a direction perpendicular to the stripes of magnetic anomalies, whereas the amplitude response is weak and the slope of the logarithmic spectrum is small in a direction parallel to the stripes of magnetic anomalies. The depth estimates in the perpendicular direction are close to the actual values, whereas the depths estimates in the parallel direction are significantly lower than the actual values. The actual marine magnetic anomalies of the South China Sea exhibit an anisotropic power spectrum that is consistent with the spectral anisotropy of magnetic anomalies of the synthetic fractal striped magnetization models.
EN
Analysis of rainfall data from the island of Crete, Greece was performed to identify key hydrological years and return periods as well as to analyze the inter-annual behavior of the rainfall variability during the period 1981–2014. The rainfall spatial distribution was also examined in detail to identify vulnerable areas of the island. Data analysis using statistical tools and spectral analysis were applied to investigate and interpret the temporal course of the available rainfall data set. In addition, spatial analysis techniques were applied and compared to determine the rainfall spatial distribution on the island of Crete. The analysis presented that in contrast to Regional Climate Model estimations, rainfall rates have not decreased, while return periods vary depending on seasonality and geographic location. A small but statistical significant increasing trend was detected in the inter-annual rainfall variations as well as a significant rainfall cycle almost every 8 years. In addition, statistically significant correlation of the island’s rainfall variability with the North Atlantic Oscillation is identified for the examined period. On the other hand, regression kriging method combining surface elevation as secondary information improved the estimation of the annual rainfall spatial variability on the island of Crete by 70% compared to ordinary kriging. The rainfall spatial and temporal trends on the island of Crete have variable characteristics that depend on the geographical area and on the hydrological period.
PL
Artykuł dotyczy analizy działania obwodu elektrycznego stanowiska do badania elektroizolacyjnego sprzętu ochronnego. Podczas pracy stanowiska stwierdzono, że napięcie probiercze jest znacznie odkształcone. Aby poznać przyczyny zniekształceń wykonano pomiary sygnałów napięcia i prądu w trzech miejscach obwodu. Ciągi próbek sygnałów poddano analizie widmowej i wyznaczono charakterystyki elementów układu. Analiza wyników pozwoliła stwierdzić, że przyczyną zniekształceń jest praca jednego z transformatorów w stanie nasycenia. Można zaobserwować zjawisko ferrorezonasu prądów powodujące znaczne ich zniekształcenie. Drugim zaobserwowanym niekorzystnym zjawiskiem jest rezonans napięć powodujący wzmocnienie wybranych harmonicznych.
EN
This article deals with the analysis of the electrical circuit of the electrical insulating equipment inspection stand. The test stand consists o f two transformers, the TRS-10 regulator and the TP-60 tester. The test voltage can be adjusted from 0 to 30 KV. During the operation of the station it was found that the test voltage is significantly deformed. In order to know the causes of distortion, measurements of voltage and current signals were made at three locations of the circuit. Signal samples were subjected to spectral analysis and the characteristics of system components were designated. Analysis of the results showed that the cause of the distortion is the operation of one of the transformers in the saturation state. The signals of currents obtained for different settings of the transformer have a deformed waveform (fig. 2), typical of the ferroresonance phenomenon. The occurrence of this phenomenon confirms the course of the characteristic (Fig. 4). The second observed unfavorable phenomenon is resonance of voltages in the high voltage circuit, resulting in the strengthening of selected harmonics of voltage. This phenomenon can be observed on the basis of the shape of frequency characteristics of the loaded test transformer TP-60 (Fig. 6).
17
Content available remote EEG spectral analysis of human cognitive workload study
EN
The paper presents an experiment performed in order to confirm the hypothesis that the level of human cognitive workload can be studied by spectral anal-ysis. The experiment contained intervals ensuring high cognitive load. They were dis-played alternately with relaxing breaks. The spectral analysis covered changes in EEG bands including the alpha/theta ratio.
PL
Artykuł przedstawia wyniki eksperymentu, który został zrealizowa-ny w celu potwierdzenia hipotezy, że poziom obciążenia poznawczego można zbadać za pomocą analizy widmowej sygnału EEG. Eksperyment złożony był z interwałów zapewniających badanym wysokie obciążenie poznawcze (zadania matematyczne), wyświetlanych na przemian z interwałami relaksującymi. Analiza widmowa objęła fa-le EEG włączając w to stosunek alpha/theta.
18
Content available remote Zastosowanie widm wyższych rzędów do analizy sygnałów napięcia spawania
PL
W artykule zaprezentowano wyniki badań nad zastosowaniem widma trzeciego rzędu do analizy sygnałów napięcia spawania. Widma wyższych rzędów w przeciwieństwie do powszechnie stosowanego widma mocy sygnału zachowują informację o zależnościach fazowych i pozwalają w pełni scharakteryzować niestabilności procesu spawania, co potwierdzają przeprowadzone badania.
EN
The article presents results of research on the application of third-order spectrum to analysis of the welding voltage signals. Higer-order spectra in contrast to the commonly used power spectrum carry information phase and allow to fully characterize the instability of the welding process which is confirmed by studies carried out.
PL
W systemach ciągłego monitoringu połączeń spawanych konstrukcji cienkościennych, najbardziej obiecującą jest metoda wibrodiagostyczna. Najważniejszą jej zaletą jest to, że jest efektywna i stwarza największe możliwości badań w czasie rzeczywistym. W pracy zastosowano metodę pomiarów charakterystyk dynamicznych konstrukcji przy pomocy czujników piezoelektrycznych. W artykule przedstawiono założenia oceny połączeń spawanych z wykorzystaniem analizy logarytmicznego rozkładu wartości średniej widm amplitudowych obliczanych metodą okien czasowych. Wykorzystana miara statystyczna w postaci wartości średniej jest propozycją parametru, którego analiza dla danego połączenia spawanego może pozwolić na jednoznaczną ocenę jego jakości. Zwrócono uwagę na istotne dla badania elementy, przedstawiono algorytm obliczeniowy oraz przykładowe wyniki z aplikacji proponowanej metody do kilku wybranych płyt spawanych z różnymi rodzajami wad. Z przeprowadzonych badań wynika, że analiza rozkładów wartości średnich dla widm amplitudowych obliczonych metodą okien czasowych wskazuje, że różnią się one między sobą w zależności od spawów, wskazując na ich jakość i wady, które są z nimi związane.
EN
In continuous monitoring systems of welded joints of thin-walled structures, a vibrodiagnostic method is the most promising. Its most important advantage is that it is effective and offers the greatest real-time research capabilities. It is used in elassic NDT techniques as well as in construction monitoring during operation. This work presents a measurement method of dynamic characteristics of the structure with the use of piezoelectric sensors. The article presents the assumptions concerning the evaluation of welded joints using the analysis of the logarithmic distribution of the amplitude spectrums calculated by the time window method. The statistical measure used in the form of the mean value is a proposed parameter, which analysis for a given welded joint may enable an unambiguous assessment of its quality. Attention was paid to the elements important for the study and they included a calculation algorithm and the sample results from the proposed method used for some selected plates with different welds. The work contains the description of the stand to register dynamic characteristics in case of welded joints. The results of the tests show that the analysis of the logarithmic distribution value for amplitude spectrums calculated by the time window method indicates that they differ markedly depending on the welds, indicating their quality and defects which are associated with them.
20
Content available remote Wieloaspektowa analiza spektralna sygnałów fonokardiograficznych
PL
W artykule przedstawiono koncepcję analizy spektralnej sygnałów fonokardiograficznych. Zaprezentowano wyniki analizy sygnałów zawierających od kilku do kilkunastu uderzeń serca oraz sygnałów krótkich zawierających pojedyncze uderzenie serca. Przedstawiono propozycje kilkudziesięciu widmowych cech dystynktywnych oraz ocenę ich przydatności w diagnostyce schorzeń kardiologicznych.
EN
The article presents the idea of spectral analysis of phonocardiographic signals. The results of analysis of signals containing from several to over a dozen heartbeats and short signals containing only one heartbeat. Proposals dozens of spectral distinctive features and evaluate their usefulness in the diagnosis of cardiac diseases.
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