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EN
In this paper, the effects of the power modulation on atmospheric pressure plasma jet, operated in Ar+2%N2 mixture, are studied. Time resolved optical emission spectroscopy is used for the investigation. From line and band intensities, the excitation, vibration and rotation temperatures are calculated. Their evolution during the modulation period exhibits a strong dependence on modulation frequency. For higher modulation frequencies, there is significant discrepancy in rotational temperatures calculated from OH spectra and from N2+ spectra, which indicates that thermalisation time can reach milliseconds.
EN
The specific working conditions of the wind turbine in strong wind cause a number of problems in the measurement of noise indicators used in its short and long-term assessment. The wind is a natural working environment of the turbine, but it also affects the measurement system, moreover, it can be a secondary source of other sounds that interfere with the measurement. One of the effective methods of eliminating the direct impact of wind on the measurement system is placing the microphone on the measurement board at ground level. However, the obtained result can not be directly compared with the admissible values, as it has to be converted to a result at a height of 4 m. The results of previous studies show that this relation depends, inter alia, on the speed and direction of the wind. The paper contains the results of measurements on the measurement board, according to EN 61400-11:2013, and at a height of 4 m above ground made simultaneously in three points around the 2 MW turbine at various instantaneous speeds and changing wind directions. Analysis of the impact of measuring point location on the measurement result of noise indicators and the occurrence of additional features affecting the relationship between the values measured on the board and at the height of 4 m, and especially the tonality, amplitude modulation and content of low frequency content, was made.
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Content available remote Computer simulation of modulated two-beam interference using monochromatic light
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EN
Two different models are suggested to describe the fringe shift obtained from the two beam interference modulated by the phase variations of transparent objects. The first model of the fringe shift assumes a linear triangular distribution, while the second model varies as a truncated Gauss function. The Abel transform enables computation of the refractive index distribution from the theoretical data of the fringe shift. The fringe shift of the phase object is represented in the harmonic term of the intensity distribution formula. A computer program is written to plot both of the fringe shifts of the models described and the corresponding refractive indices of the phase object. Comparative results are cited in the introduction which are based on an algebraic reconstruction technique (ART) using two models; one of them has a cosine phantom field which constructs an asymmetric single peak, while the other model has cosGauss function giving an asymmetric double-peak phantom. These results are compared with our results, which gives only a single peak in both cases of linear and quadratic variations, which is convenient for use in optical fibers.
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Content available remote Detection of asynchronicity in the amplitude modulation domain
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EN
A just noticeable time delay (JNTD) between the onset of a single sinusoidal amplitude modulation (AM) and a complex modulation applied to the same carrier was measured in this study. The carrier was a 4-kHz tone and the modulator was a five-component multitone complex. In the first experiment, four of five components had constant frequencies, i.e. 160, 170, 180, 190 Hz and they were turned on synchronously (synchronous components) in the middle of the carrier duration. The frequency of the fifth component (asynchronous one) varied from 10 to 150 Hz and it was turned on earlier than the synchronous ones. In the second experiment, the asynchronous component was situated in the centre of the synchronous components' spectrum; its frequency was constant and equal to 100 Hz. The spectral separation between the asynchronous component and the synchronous ones of the modulator varied. The results, i.e. the just noticeable time delay between the onset of a single sinusoidal amplitude modulation and a complex modulation (or asynchrony threshold), are analogous to those obtained in the audible frequency domain. They can be interpreted on the basis of the auditory system model containing a bank of modulation filters. It seems that two separate mechanisms are responsible for the JNTD between the onset of the single component modulation and the complex modulation. The first one results from an interaction between all the components of a modulator passing a single modulation filter tuned to the frequency of the asynchronous component. This sort of interaction (or masking) was most effective when the spectral separation between the asynchronous component and the synchronous ones was the smallest one. With an increase in this separation, a significant decrease in the asynchrony thresholds was observed. The second mechanism determining the obtained asynchrony thresholds is based on the uncertainty principle: modulation filters with good frequency selectivity, i.e. filters tuned to low modulation rates, are characterised by a poor time resolution. Thus, in the case of the lowest frequencies of the asynchronous component the subjects' performance would be relatively poor even when there was a significant spectral interval between this component and the synchronous ones. As in the audible frequency domain, the pattern of the asynchronicity thresholds was related to the modulation filter bandwidth. The obtained results suggest the bandwidth of the modulation filters whose Q factor should be close to 1 or less.
5
Content available remote On discrete Fourier spectrum of randomly modulated signals
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EN
In this work the problem of characterization of Discrete Fourier Transform (DFT) spectrum of an original complex-valued signal modulated by random fluctuations of amplitude and phase is investigated. It is assumed that the amplitude and phase of signal values at discrete time moments of observations are distorted by adding realizations of independent and identically distributed random variables. The obtained results of theoretical analysis of such distorted signal spectra show that only in the case of amplitude modulation the DFT spectrum of the modulated bounded signal can be similar to the original signal spectrum, although there occur random deviations. On the other hand, if phase modulation is present, then the DFT spectrum of the modulated bounded signal not only shows random deviations but also amplitudes of peaks existing in the original spectrum are diminished, and consequently similarity to the original signal spectrum can be significantly blurred.
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Content available remote Monaural and binaural detection thresholds of amplitude modulation
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EN
This study is concerned with the amplitude modulation (AM) detection thresholds for monaural and binaural listening. In the first experiment, using a Two-Alternative Forced-Choice (2AFC) method with an adaptive procedure 2-up 1-down, the monaural and binaural AM detection thresholds were measured. Sinusoidal carrier at a frequency of 160, 500, 1000 or 4000 Hz was amplitude-modulated by a single sinusoidal modulator at a frequency of 4, 32, 64 or 128 Hz. Due to a significant intersubject scatter of the results it was impossible to estimate the difference between the thresholds determined for monaural and binaural presentation of the stimuli. Therefore, in the next experiment, psychometric functions for AM detection for both monaural and binaural listening were determined. This experiment was carried out for sinusoidal carriers at frequencies of 5000, 2000 and 6000 Hz and for sinusoidal modulator at frequencies of 4, 64 and 128 Hz. The results of this experiment showed a statistically significant difference between slopes of the psychometric function (after the percent of correct responses was converted to the detectability, d', domain) for monaural and binaural stimuli presentation. Assuming that the AM threshold coincided with d' = 1 it can be stated that monaural and binaural AM thresholds are significantly different.
EN
This article concerns with a new model of the sound envelope processing in the auditory system. The so-called non-negative-impulse-response (NNIR) modulation filters concept argues that if any form of the acoustic signal envelope filtering took place in the auditory pathway, this process should not be described in terms of a band-pass filtration. This modification of the traditional model of the auditory system temporal resolution, based on the modulation filterbank (MFB) activity, results from the cardinal property of the sound envelope and its neural representation, i.e. neural discharges period histogram, which are unavoidably unipolar signals of non-negative values. It has been assumed that if hypothetical modulation filters existed, they should be characterised by a non-negative-impulse-response and, consequently, the frequency characteristics of such filters might not reveal the band-pass properties. The results of the model investigations are compared with selected psychophysical and physiological data.
EN
The possibility of a normal distribution indicates that few particles are in the same phase during a breath and their reflections can be observed on the chest wall, then a few explosive waves with relatively large power occurr occasionally. Therefore, the one-cycle sine wave which is simulated as a single burst of the explosive effect phenomenon penetrates through the chest wall and was analysed to explore the reason of the crackle sounds. The results explain the differences between the definitions of crackle proposed by Sovijärvi et al. (2000a). The crackles in the lungs were synthesised by a computer simulation. When the coarse crackles occur, the results indicate that higher burst frequency carriers (greater than 100 Hz) directly penetrate the bandpass filter to simulate the chest wall. The simulated coarse crackle sounds were low pitched, with a high amplitude and long duration. The total duration was greater than 10 ms. However, for a lower frequency carrier (approximately 50 Hz), the fundamental frequency component was filtered out. Therefore, the second harmonic component of the lower frequency carrier, i.e., the fine crackle, penetrated the chest wall. Consequently, it is very possible that the normal lung sounds may contain many crackle-shaped waves with very small amplitudes because of the filtering effects of the chest wall, environment noises, electric devices, stethoscopes, and human ears, the small crackles disappear in the auscultations. In addition, our study pointed out that some unknown crackles of the very low frequency under the bandwidth of the human ears cannot penetrate the airways and be detected by medical doctors. Therefore, it might be necessary to focus advanced electronic instrumentation on them in order to analyse their possible characteristics for diagnosis and treatment of the respiration system.
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Content available remote Modulation masking for recurrent low-noise noise masker
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EN
The main purpose of these investigations was to examine modulation masking phenomenon for recurrent low-noise noise masker. Such masker is characterized by three parameters, namely: repetition frequency, frep, centre frequency, fo, and bandwidth, b. The parameter frep is not reflected in the signal power spectrum and is related to the autocorrelation period. The parameters fo and b describe spectral properties of the interfering signal, i.e. localization and concentration of its power in the frequency domain. In order to separate possible effects of the masker temporal repetition and its spectral parameters, modulation masking measurements were carried out for fo=64 Hz, b=16 Hz and frep=1 s-1 (without repetition), 4 s-1 and 8 s-1 and probe signal of frequencies fp=1, 2, 4, 6, 8, 12, 16, 32, 52 and 64 Hz. The masker rms modulation depth was 30%; carrier signal was a 4-kHz sinusoid. The main conclusion is that modulation masking patterns are determined by the spectral properties of the masker.
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Content available remote Bispectral Analysis in Vibroacoustic Diagnostics of Gears
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EN
The work concerns diagnosis of the origins and development of early stages of defects based on information found in the vibroacoustic signal. At the beginning the necessity of selection of diagnostic parameters dependent upon the amount of dissipated energy and related defect development is proven. Assuming that the basic role in transmission of such diagnostic information is played by the phenomena of amplitude and phase modulation of the vibroacoustic signal and non-linear effect of system, it is points to the significance of the signal non-linear components. For that reason in this work a model of signal in the form of a Volterra series is assumed, which enables examination of the influence that disturbances have upon non-linear components. On the basis of exemplary analysis of the contact condition disturbances, the possibility of generation of a bilinear component is presented. What serves this purpose is the model of non-linear and instantaneous contact. Simultaneously problems of selection of signal analysis methods that enable realisation of assumed aims are presented. Emphasising the fact that defect development does not always lead to a significant growth of the vibroacoustic signal power, the author has shown importance of methods of higher-order spectral analysis like, bispectrum and Wigner's distribution.
EN
Analysis of the phenomenon of modulation of vibroacoustic signal's parameters, especially the amplitude and the frequency structure of the envelope which is directly associated with the occurrence of group velocity, may prove to be an effective tool for diagnosing the technical condition of pre-stressed structures. This scope of work and the examination of the influence of local defects and of the environmental impact was the main research task during COST Action 534 project duration. An issue that is particularly interesting and that calls for additional analyses and experiments will be the development and adaptation of effective de-modulation algorithms.
PL
Analiza zjawiska modulacji wibroakustycznych parametrów sygnału, a w szczególności amplitudy i struktury częstościowej obwiedni, która jest bezpośrednio związana ze zjawiskiem prędkości grupowej, może być efektywnym narzędziem w diagnozowaniu stanu technicznego struktur sprężonych. Ten zakres pracy, jak również badanie wpływu występowania miejscowych wad było głównym zadaniem kończącej się Akcji COST 534. Zadaniem, szczególnie interesującym i wymagającym dalszych analiz i eksperymentów, jest rozwój i adaptacja użytecznych algorytmów demodulacji.
PL
Zaprezentowano wysokosprawny kluczowany zasilacz sterowany sygnałem akustycznym (50 Hz...5 kHz) do modulatorów amplitudy przebiegów w. cz. o dużej mocy do nadajników radiowych z modulacją AM. Zastosowano konwerter DC-DC obniżający napięcie (buck), w którym zmienny sygnał modulujący jest sumowany z napięciem odniesienia DC, a dzięki pętli sprzężenia zwrotnego o dużym wzmocnieniu napięcie wyjściowe jest proporcjonalne do wypadkowego napięcia odniesienia. Stabilność i szerokie pasmo przenoszenia zasilacza sterowanego uzyskano, stosując mieszaną kompensację (lag-lead) charakterystyk częstotliwościowych bloków pętli.
EN
A high-efficiency switched-mode supply unit controlled by the extemal audio signal (50 Hz... 5 kHz), destined for high-power amplitude modulators of h.f. carrier in radio AM transmitters is presented. This supply unit is based on the buck DC-DC converter in which the modulating audio signal is summed with the DC reference voltage. Due to high-gain feedback loop the output voltage is proportional to the resultant reference voltage. The stability of the controllable supply unit and the wide band of modulating audio signals have been obtained by the lag-lead compensation of frequency characteristics of the feedback loop.
13
Content available MultiDot - nowa idea rastrowania AM
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EN
Screening technology let reproduce continuous tone images using bilevel printing method (as f.e. offset). Some properties of human eye allows the correct reception of the continuous tone image. One have to remember, that tonal value (caused by surface covered by printing elements only) existing on the printing plateis not the same as the one present on the printout. In offset printing technology the difference between tonal value on the printing plate and on the printout is provoked by two different phenomenons: one is the DotGain, while the other is caused by driving the ink out by dampening solution. The DotGaineffecthas 3 mainreasons: – spilling out of the ink on the printedsurface, – deformation of transfer medium (f.e. offset blanket) – present only when indirect printing technology is in use – “shadow” of the printing inklayer, ... and iswelldefined and known. The mutual (the ink and the water/dampening solution) influence is very difficult to predict using mathematic formulas. We can observe, that (because of the DotGain effect) there are some areas not covered by ink, but absorbing the light as they would be – so it can be a base for some ink saving – if the effect would be used properly. However the FM screening has significant DotGain effect (so ink saving should be noticeable), it demonstrates lot of disadvantages: less print stability, unevenly flat areas and many, many others. To fulfill some expectations the new AM screening was developed (and patented). It was named MultiDot and is based on multi-cluster principle, where – what’s important – single clusters have different size and shape. Optimal shape and tonal function caused, that newly developed screening concept let the user receive stable, rich in details and Moire free images with significant ink-saving capabilities. The other aspect of using MultiDot screening structure is to prevent prints against illegal copying and allowing the user to confirm (or deny) the authenticity of certain printouts or goods – this functionality is called MultiDot Security and will be a subject of another article.
PL
W artykule omówiono definicję wskaźnika ΔV10. Zaproponowano schemat blokowy miernika ΔV10 i wyznaczono jego równanie przetwarzania dla sinusoidalnej zmienności napięcia. Porównano wartości wskaźników ΔV10 i Pst. Prezentując wyniki porównań obu miar przybliżono możliwości diagnostyczne wskaźnika ΔV10. Odwołując się do zamieszczonych zależności ΔV10, Pst i ƒm wykazano, że dla zmienności napięć występujących w sieciach elektroenergetycznych niemożliwe jest przeliczanie jednej miary do drugiej.
EN
The ΔV10 index is a measure of voltage fluctuations in power grids proposed by the Japanese CRIEPI Institute [1] and used all over the Far East countries. European standards prefer Pst and Plt indicators in voltage fluctuation measurements [11]. The ΔV10 and Pst/Plt are different in terms of the characteristics of measurement signal chains [6]. Therefore the measures may be characterized by different diagnostic capabilities. This may lead to the situation where some receivers may be described as faultless while voltage fluctuations are acceptable for one measure and may be described as faulty with the voltage fluctuations being unacceptable for the other measure. On the other hand, some level of uncertainty may appear as the influence of a receiver may be classified as obnoxious with the use of one measure and not-obnoxious with the use of the other. The paper includes analytical determination of the ΔV10 index value dependency on the voltage fluctuation reproduced with a sinusoidal amplitude modulation (Eq. (2)). The calculations have been made for the assumed signal chain model of a ΔV10 index measuring instrument (Fig. 3). The values of ΔV10 and Pst indexes at a given sinusoidal voltage fluctuation have been compared (Figs. 4-6). On the basis of the obtained ΔV10 and Pst dependencies on ƒm it has been assumed that for the voltage fluctuations present in power grids of unknown type and frequency it is impossible to convert one measure into the other.
PL
W pracy przedstawiono zagadnienie oceny stanu technicznego struktury sprężonej ze szczególnym uwypukleniem możliwości wykorzystania efektów modulacji amplitudowej występujących w obserwowanym sygnale wibroakustycznym. Podstawą takiego podejścia jest teza że zmianie rozkładu naprężeń w przekroju poprzecznym struktury sprężonej towarzyszy mierzalna zmiana parametrów sygnału wibroakustycznego.Wynika ona z założenia, że wraz z wywołaniem stanu sprężenia wstępnego w zginanej konstrukcji zachodzi zjawisko dyspersji, a tym samym zmiana parametrów propagacji fali, w szczególności występowanie mierzalnej różnicy wartości prędkości fazowej i grupowej.Analiza relacji między stanem naprężeń a wartościami prędkości fazowej i grupowej stwarza możliwość budowania diagnostycznych modeli odwrotnych i wyznaczania ilościowych zmian takich parametrów stanu technicznego, jak siły sprężające, moduł Younga czy naprężenia panujące w konstrukcji. Praca powstała na podstawie rozprawy doktorskiej autora.
EN
The paper presents the issue of assessment of the technical condition of a prestressed structure while particularly underscoring the possibilities offered by amplitude modulation effects which are found in the observed vibroacoustic signal. The basis for such an approach is the thesis that change of distribution of stress in the cross-section of a prestressed structure is accompanied by a measurable change of the parameters of a vibroacoustic signal.The thesis stems from the assumption that the condition of prestressing of a structure, as it is being bent, is accompanied by the phenomenon of dispersion and hence of the change of wave propagation parameters, especially the occurrence of a measurable difference between the values of phase and group velocities.Analysis of the relations between the state of stress and the values of phase and group velocities creates the possibilities of developing the reverse diagnostic models and determining the quantitative changes of such parameters of technical condition as compressive forces, Young's modul or the stress in the structure. The paper has been developed on the basis of the author's Ph.D. thesis.
EN
The operation of a wind turbine (WT) is characterized by fluctuations in sound pressure amplitude associated with the passage of the propeller blade through the tower. Amplitude Modulation (AM) is one of the factors that contributes to the increased annoyance of wind turbine noise. The phenomenon of AM is currently the subject of research in many research centers around the world in the context of a parametric assessment of its impact on annoyance. Despite the development of many methods to measure the AM of a WT noise, there is no commonly accepted method. This paper discusses the most crucial factors that stimulate the phenomenon of AM and the implementation in the MATLAB environment of the algorithm to find the frequency and depth of AM proposed by the Amplitude Modulation Working Group (AMWG). The results of verification of the developed algorithm as well as the measurement results of the frequency and depth of modulation for two measurement samples of a 2 MW wind turbine are presented.
EN
The purpose of this paper is to develop a method of forecasting and analysis of high-cycle (HCF) resistance to fatigue relying on vibroacoustic signal analysis. It proposes using the results of vibroacoustic signal analysis obtained during accelerated fatigue tests conducted in dedicated test bed constructed specially for this purpose and operating in the frequency range of 10 kHz which corresponds to the proper frequency of vibration of samples. Thanks to the small dimensions and mass, the test bed can be located on the vibration inductor, which enable investigations of the amplitude modulation's influence. Additionally, it's described a problem of, phenomena oriented, diagnostics information's detection.
PL
Celem pracy jest opracowanie metody prognozowania i analizy wysokocyklowej (HCF) trwałości zmęczeniowej na podstawie badania sygnału wibroakustycznego. Proponuje się wykorzystać wyniki analizy sygnału wibroakustycznego, uzyskiwane podczas przyspieszonych badań zmęczeniowych, prowadzonych na specjalnie do tego celu skonstruowanym i zbudowanym stanowisku badawczym, pracującym w zakresie częstotliwości rzędu 10 kHz, odpowiadającym częstotliwości drgań własnych próbek. Dzięki małym wymiarom i masie stanowisko badawcze może być umieszczone na wzbudniku drgań, co umożliwia badanie wpływu modulacji amplitudy. Dodatkowo opisano zagadnienie detekcji informacji diagnostycznej, zjawiskowo zorientowanej. Publikacja opracowana na podstawie badań wykonywanych w ramach projektu "Monitorowanie Stanu Technicznego Konstrukcji i Ocena jej żywotności" (MONIT). Projekt współfinansowany ze środków Europejskiego Funduszu Rozwoju Regionalnego w ramach Programu Operacyjnego Innowacyjna Gospodarka (PO IG 1.2)
PL
Powszechne nazywanie modulacji liniowych nośnej sinusoidalnej modulacjami amplitudy nie jest uzasadnione, bowiem modulacji obwiedni zwykle towarzyszy modulacja kąta. Istnieją nawet przypadki, kiedy efektywnie modulowany jest tylko kąt. Rzeczywistą modulacją amplitudy jest wyłącznie modulacja AM. Przyczynami klasyfikacyjnych niedostatków są: historia wynalazków, nie dość konsekwentne interpretowanie pojęcia amplituda i niepostawienie pytania o efekt modulacji amplitudy, która powinna wytwarzać nośną zmodulowaną tylko w amplitudzie. Te dwie ostatnie przyczyny są szczegółowo rozważone w artykule, w którym także zasugerowano pewne zmiany w nazewnictwie. Ponadto w sytuacji specyficznego zakłócenia porównano odbiory homodynowy i heterodynowy. Zaproponowano sekwencję niektórych tematów prezentacji problematyki modulacji liniowych.
EN
Linear modulations of a sinusoidal carrier are usually described as amplitude modulations which is not a proper choice, since an envelope modulation is often accompanied by an angle modulation. There are even some cases, when only the angle is modulated effectively. The actual amplitude modulation is the modulation marked with an acronym AM. The classification and the naming misfits result from three reasons: history of inventions, a lack of a consequent interpretation of the term amplitude and not raising the question on an effect of the amplitude modulation which should produced amplitude only modulated carrier. The last two reasons are considered in the paper in detail. Some naming changes are suggested. Furthermore, for a specific interference the homodyne and the heterodyne receptions are compared. There is a proposal of a sequence of problems explaining concepts of linear modulations.
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