scholarly journals A few observations on the amplitude spectra of Ponzo Illusion stimuli

2019 ◽  
Author(s):  
Bernt Skottun
Keyword(s):  
Amplitude Spectrum ◽  
Visual Stimuli ◽  
Ponzo Illusion ◽  
Spatial Filter ◽  
Amplitude Spectra

Ponzo Illusion stimuli were filtered with a spatial filter centered on either the upper (the bar closer tothe oblique lines) or lower bar (the bar farther from the oblique lines). It was found that the image filteredwith the filter centered on the upper bar had an amplitude spectrum consistent with the perception of alonger bar relative to the spectrum of the image filtered with the filter centered on the lower bar. This isin agreement with the Ponzo Illusion. Interference was assessed by comparing the amplitude spectrum ofthe filtered oblique lines plus the amplitude spectrum of a filtered bar versus the spectrum of the filteredimage of the two stimuli together. This analysis showed that interference, which takes place in the stimuliand does not depend on vision, may not only cause amplitude reductions but may also cause the shape ofthe amplitude spectra to be altered. In the present case the changes in the spectra were consistent with thechanges in perceived length experienced in the Ponzo Illusion. This suggests, therefore, that interferencemay have the potential to alter the appearance of visual stimuli.

Determination of crustal thickness from spectral behavior of SH waves

1969 ◽  
Vol 59 (3) ◽  
pp. 1247-1258
Author(s):  
Abou-Bakr K. Ibrahim
Keyword(s):  
Amplitude Spectrum ◽  
Body Waves ◽  
Multiple Reflections ◽  
Matrix Formulation ◽  
Sh Waves ◽  
Crustal Model ◽  
Amplitude Spectra ◽  
Phase Spectra ◽  
Zero Phase

abstract The amplitude spectrum obtained from Haskell's matrix formulation for body waves travelling through a horizontally layered crustal model shows a sequence of minima and maxima. It is known that multiple reflections within the crustal layers produce constructive and destructive interferences, which are shown as maxima and minima in the amplitude spectrum. Analysis of the minima in the amplitude spectra, which correspond to zero phase in the phase spectra, enables us to determine the thickness of the crust, provided the ratio of wave velocity in the crust to velocity under the Moho is known.

The Effect of Directional Spreading on Interaction of Focused Wave Groups With a Cylinder

2004 ◽  
Author(s):  
Eugeny V. Buldakov ◽  
Rodney Eatock Taylor ◽  
Paul H. Taylor
Keyword(s):  
Numerical Solutions ◽  
Amplitude Spectrum ◽  
Wave Group ◽  
Helmholtz Equations ◽  
Incoming Wave ◽  
Wave Groups ◽  
Practical Applications ◽  
Amplitude Spectra ◽  
Focused Wave ◽  
Focused Wave Group

The problem of diffraction of a directionally spread focused wave group by a bottom-seated circular cylinder is considered from the view point of second-order perturbation theory. After applying the time Fourier transform and separation of vertical variable the resulting two-dimensional non-homogeneous Helmholtz equations are solved numerically using finite differences. Numerical solutions of the problem are obtained for JONSWAP amplitude spectra for the incoming wave group with various types of directional spreading. The results are compared with the corresponding results for a unidirectional wave group of the same amplitude spectrum. Finally we discuss the applicability of the averaged spreading angle concept for practical applications.

scholarly journals Object Clusters or Spectral Energy? Assessing the Relative Contributions of Image Phase and Amplitude Spectra to Trypophobia

2019 ◽  
Author(s):  
R. Nathan Pipitone ◽  
Chris DiMattina
Keyword(s):  
Amplitude Spectrum ◽  
Spectral Energy ◽  
Visual Comfort ◽  
Visual Discomfort ◽  
Comfort Levels ◽  
Spatial Frequencies ◽  
Amplitude Spectra ◽  
Small Clusters ◽  
Full Factorial ◽  
Phase Spectra

Trypophobia refers to the visual discomfort experienced by some people when viewing clustered patterns (e.g., clusters of holes). Trypophobic images deviate from the 1/f amplitude spectra typically characterizing natural images by containing excess energy at mid-range spatial frequencies. While recent work provides partial support for the idea of excess mid-range spatial frequency energy causing visual discomfort when viewing trypophobic images, a full factorial manipulation of image phase and amplitude spectra has yet to be conducted. Here, we independently manipulated the phase and amplitude spectra of 31 Trypophobic images using a standard Fast Fourier Transform (FFT). Participants rated the four different versions of each image for levels of visual comfort, and completed the Trypophobia Questionnaire (TQ). Images having the original phase spectra intact (with either original or 1/f amplitude) explained the most variance in comfort ratings and were rated lowest in comfort. However, images with the original amplitude spectra but scrambled phase spectra were rated higher in comfort, with a smaller amount of variance in comfort attributed to the amplitude spectrum. Participant TQ scores correlated with comfort ratings only for images having the original phase spectra intact. There was no correlation between TQ scores and comfort levels when participants viewed the original amplitude / phase-scrambled images. Taken together, the present findings show that the phase spectrum of trypophobic images, which determines the pattern of small clusters of objects, plays a much larger role than the amplitude spectrum in determining visual comfort.

The thickness imaging of channels using multiple-frequency components analysis

2019 ◽  
Vol 7 (1) ◽  
pp. B1-B8 ◽  
Author(s):  
Yan Ye ◽  
Bo Zhang ◽  
Cong Niu ◽  
Jie Qi ◽  
Huailai Zhou
Keyword(s):  
Amplitude Spectrum ◽  
Low Frequency ◽  
Blue Color ◽  
Self Organizing Map ◽  
Multiple Frequency ◽  
Thickness Estimation ◽  
Red Color ◽  
Amplitude Spectra ◽  
Frequency Components ◽  
Components Analysis

Blending of different frequency components of seismic traces is a common way to estimate the relative time thickness of the formation. Red, blue, and green (RGB) color blending is one of the most popular blending models in analyzing multiple seismic attributes. Geologists and geophysicist interpreters typically associate low-frequency components (formations with the largest thickness value) with a red color, medium-frequency components (formations with a medium thickness value) with a green color, and high-frequency components (formations with the smallest thickness value) with a blue color for the thickness estimation of thin beds using frequency components. However, we found that the same result of RGB blending may come from different sets of three frequency components. As a result, the same blended color may correspond to several different time thicknesses. It is also very difficult to interpret the corresponding thickness of the blended colors such as white and yellow. To avoid the ambiguity of time-thickness estimation using RGB blending, we have estimated the time thickness of the thin beds using all of the frequency components in a user-defined frequency band instead of only three frequency components. Our workflow begins with the normal seismic spectral decomposition. Considering that the different reflectivity pairs with a different time thickness have a different amplitude spectrum, we then use the self-organizing map to cluster the decomposed amplitude spectra of seismic traces. We finally assign each cluster with a relative thickness by comparing the clustered results with well logs.

scholarly journals An Experimental Study of Focusing Wave Generation with Improved Wave Amplitude Spectra

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2521 ◽  
Author(s):  
Guochun Xu ◽  
Hongbin Hao ◽  
Qingwei Ma ◽  
Qinqin Gui
Keyword(s):  
Wave Energy ◽  
Wave Amplitude ◽  
Wave Spectrum ◽  
Amplitude Spectrum ◽  
Wave Frequency ◽  
Wave Crest ◽  
Wave Component ◽  
Frequency Wave ◽  
Motion Signal ◽  
Amplitude Spectra

We experimentally investigate the generating results of space-time focusing waves based on two new wave spectra, i.e., the quasi constant wave amplitude spectrum (QCWA) and the quasi constant wave steepness spectrum (QCWS), in which amplitude and steepness for each wave component can be adjusted with fixed wave energy. The wavemaker signal consists of a theoretical wavemaker motion signal and two different auxiliary functions at two ends of the signal. By testing a series of focusing waves in a physical wave tank, we found that with given wave energy, the QCWA spectrum can produce a focusing wave with larger crest elevation and farther focusing location from the wavemaker flap, as compared with the QCWS spectrum. However, both spectra lead to larger focusing wave crests when the wave frequency bandwidth was narrowed down and a positive correlation between the generated relative wave crest elevation and the input wave elevation parameter. The two spectra produce different focusing wave positions for the same wave frequency range. We also found that the focusing time strongly relates to the energy of the highest-frequency wave component of the wave spectrum.

scholarly journals Is the Tilt-Illusion in the stimuli?

2018 ◽  
Author(s):  
Bernt Skottun
Keyword(s):  
Visual System ◽  
Present Report ◽  
Visual Stimuli ◽  
Orientation Tuning ◽  
Tilt Illusion ◽  
Amplitude Spectra

Interference between visual stimuli has been assessed mainly in regard to how such interactions mayreduce stimulus power. The question of if, or to what extent, interference may change stimuli in other wayshas been largely ignored. The present report asks if interference may alter the amplitude spectra of elongatedcontours so as cause their perceived orientations to be changed. Computations indicate that for two stimulidiffering in orientation by between 5 and 40 degrees interference is largest for orientations between the peakorientations of the two stimuli which may cause their orientation tuning functions to be ”pushed” apart.Since interference takes place in the stimuli and is independent of vision and the visual system it is possible,therefore, for the physics of stimuli to cause illusory tilt.

scholarly journals THE ATMOSPHERIC PRESSURE EFFECT ON MUON DATA NORMALIZATION BY SPECTRAL ANALYSIS STUDIES

2013 ◽  
Vol 31 (3) ◽  
pp. 507 ◽  
Author(s):  
Nivaor Rodolfo Rigozo ◽  
Adriano Petry
Keyword(s):  
Time Series ◽  
Spectral Analysis ◽  
Atmospheric Pressure ◽  
Amplitude Spectrum ◽  
Cosmic Ray ◽  
Pressure Effects ◽  
Pressure Amplitude ◽  
Analysis Method ◽  
Amplitude Spectra ◽  
Spectral Analysis Method

ABSTRACT. This paper presents a study of the atmospheric pressure effects on ground cosmic ray muon time series, using the iterative regression spectral analysis method. Along the study, it was observed that the 34 periods present in the atmospheric pressure amplitude spectrum are present in the muon data amplitude spectra as well. It was concluded that the normalization of muon data is only efficient for periods shorter than nine days, in order to eliminate the atmospheric effects.Keywords: cosmic rays, time series, spectral analysis. RESUMO. Este artigo apresenta um estudo dos efeitos da pressão atmosférica nas series temporais de raios cósmicos, usando a metodologia da análise espectral pela iteração regressiva. Foi observado um total de 34 periodicidades presentes no espectro de amplitude da pressão atmosférica que também estão presentes no espectro de amplitude dos dados de muons. Conclui-se que a padronização dos dados de muons para eliminar os efeitos da pressão atmosférica é eficiente somente para períodos abaixo de 9 diasPalavras-chave: raios cósmicos, série temporal, análise espectral.

Amplitude spectra of PcP and P phases

1968 ◽  
Vol 58 (6) ◽  
pp. 1797-1819 ◽  
Author(s):  
Goetz G.R. Buchbinder
Keyword(s):  
Amplitude Spectrum ◽  
Focal Depth ◽  
General Shape ◽  
Core Mantle Boundary ◽  
Straight Line ◽  
Short Period ◽  
Amplitude Spectra ◽  
Systematic Effects ◽  
Deep Focus

ABSTRACT Amplitude spectra were obtained from short-period PcP and P phases from seven explosions and six earthquakes. Long-period PcP and P amplitude spectra were obtained from two earthquakes. PcP and P amplitude spectra for both explosions and earthquakes are similar for any one event; therefore, station and core-mantle boundary effects are small and the general shape of the spectra is related to the source. All of the explosions studied have characteristic spectra with a pronounced minimum in the spectrum near one second. The period of this minimum increases with magnitude of the event. Short-period amplitude spectra from some intermediate- and deep-focus earthquakes resemble those from explosions. Spectra from the other earthquakes studied differ markedly from those of explosion; they have either no minimum in the spectrum near one second or very little energy for periods less than one second. The characteristics of the spectra may be of help in the classification of sources. On a plot of magnitude mb versus period of the minimum Td in the spectrum of explosions, the data form a straight line. Earthquakes with an amplitude spectrum similar to that of an explosion are randomly distributed on the plot of mb versus Td. Systematic effects of focal depth were not observed. Layering at the coremantle boundary was not detected.

Noise‐adaptive filtering of seismic shot records

Geophysics ◽  
1988 ◽  
Vol 53 (5) ◽  
pp. 638-649 ◽  
Author(s):  
Richard G. Anderson ◽  
George A. McMechan
Keyword(s):  
Fourier Transform ◽  
Adaptive Filtering ◽  
Seismic Data ◽  
Adaptive Filters ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Amplitude Spectrum ◽  
Noise Rejection ◽  
Amplitude Spectra ◽  
Spectral Subtraction Method

Ambient noise can obscure reflections on deep crustal seismic data. We use a spectral subtraction method to attenuate stationary noise. Our procedure, called noise‐adaptive filtering, is to Fourier transform the noise before the first arrivals, subtract the amplitude spectrum of the noise from the amplitude spectrum of the noisy data, and inverse Fourier transform. The phase spectrum is not corrected, but the method attenuates noise if the phase shift between the signal and noise is random. The algorithm can be implemented as a frequency filter, as a frequency‐wavenumber filter, or as two separate frequency and wavenumber filters. Noise‐adaptive filtering is often superior to conventional frequency or frequency‐wavenumber filtering because it adapts to spatial variations in the noise without parameter testing. Noise‐adaptive filters can achieve noise rejection ratios of up to 45 dB; their dynamic range is about 25 dB. These filters work best when the input signal‐to‐noise ratio is on the order of 0 dB and there are significant differences between the frequency‐wavenumber amplitude spectra of the signal and noise. Application of the method to field data can enhance events that are not visible in the input data.

Trial for Monitoring the Water Temperature Utilizing the Frequency Dependence of Reflection Coefficient of Ultrasound Passing Through Thin Layer

2019 ◽  
Vol 2 (2) ◽  
Author(s):  
Hironori Tohmyoh ◽  
Shu Terashima
Keyword(s):  
Thin Film ◽  
Reflection Coefficient ◽  
Thin Layer ◽  
Water Temperature ◽  
Acoustic Impedance ◽  
Amplitude Spectrum ◽  
Acoustic Resonance ◽  
Water Interface ◽  
Amplitude Spectra ◽  
The Difference

This paper describes a new concept to monitor the temperature of water utilizing the acoustic resonance, which occurs when ultrasound passes through a thin layer. In the ultrasonic transmission system that comprises of the reflection plate, thin film, and water, the reflection coefficient of the ultrasound at the plate/film/water interface depends on the frequency and takes its minimum value at the resonant frequency. Notably, this is closely related to the acoustic impedance of the water; moreover, it is a known fact that the acoustic impedance of the water demonstrates temperature dependence. Against this background, the present study aims to develop a technique in order to monitor the temperature of water utilizing the aforementioned correlation between the reflection coefficient and water temperature. First, a theoretical model was developed to determine the acoustic impedance of water from the difference in the amplitude spectra of echoes reflected at the back of the plate in the cases both with and without the film. It was found that the ratio of the amplitude spectrum of the echo recorded in the case with the film to that in the case without the film clearly decreased with a drop in water temperature. From this, we obtained the equation for determining water temperature experimentally. Finally, the temperature of water, which was brought down by air or ice cooling, was monitored by the proposed method. It was found that the behavior of temperature determined by the proposed method was congruent with that which was measured by a thermocouple.

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