scholarly journals Correlation plots of the Siberian Radioheliograph

2017 ◽  
pp. 17-21 ◽  
Author(s):  
Сергей Лесовой ◽  
Sergey Lesovoi ◽  
Вероника Кобец ◽  
Veronika Kobets
Keyword(s):  
Spatial Frequency ◽  
Solar Radio ◽  
Spatial Spectrum ◽  
Single Frequency ◽  
Frequency Range ◽  
The Earth ◽  
Spatial Frequencies ◽  
Siberian Solar Radio Telescope ◽  
Van Vleck ◽  
Compact Sources

The Siberian Solar Radio Telescope [Grechnev et al., 2011] is now being upgraded. The upgrading is aimed at providing the aperture synthesis imaging in the frequency range 4–8 GHz [Lesovoi et al., 2011, 2014] instead of the single-frequency direct imaging due to the Earth rotation. The first phase of the upgrading is a 48-antenna array — Siberian Radioheliograph. One type of radioheliograph data represents correlation plots [badary.iszf.irk.ru/srhCorrPlot.php]. In evaluating the covariation of two-level signals, these plots are sums of complex correlations, obtained for different antenna pairs. Bearing in mind that correlation of signals from an antenna pair is related to a spatial frequency, we can say that each value of the plot is an integral over a spatial spectrum. Limits of the integration are defined by a task. Only high spatial frequencies are integrated to obtain dynamics of compact sources. The whole spectrum is integrated to reach maximum sensitivity. We show that the covariation of two-level values accurate to Van Vleck correction is a correlation coefficient of these values.

scholarly journals Correlation plots of the Siberian Radioheliograph

2017 ◽  
Vol 3 (1) ◽  
pp. 19-25 ◽  
Author(s):  
Сергей Лесовой ◽  
Sergey Lesovoi ◽  
Вероника Кобец ◽  
Veronika Kobets
Keyword(s):  
Spatial Frequency ◽  
Solar Radio ◽  
Spatial Spectrum ◽  
Single Frequency ◽  
Frequency Range ◽  
The Earth ◽  
Spatial Frequencies ◽  
Siberian Solar Radio Telescope ◽  
Van Vleck ◽  
Compact Sources

The Siberian Solar Radio Telescope [Grechnev et al., 2011] is now being upgraded. The upgrading is aimed at providing the aperture synthesis imaging in the frequency range 4–8 GHz [Lesovoi et al., 2011, 2014] instead of the single-frequency direct imaging due to the Earth rotation. The first phase of the upgrading is a 48-antenna array — Siberian Radioheliograph. One type of radioheliograph data represents correlation plots [badary.iszf.irk.ru/srhCorrPlot.php]. In evaluating the covariation of two-level signals, these plots are sums of complex correlations, obtained for different antenna pairs. Bearing in mind that correlation of signals from an antenna pair is related to a spatial frequency, we can say that each value of the plot is an integral over a spatial spectrum. Limits of the integration are defined by a task. Only high spatial frequencies are integrated to obtain dynamics of compact sources. The whole spectrum is integrated to reach maximum sensitivity. We show that the covariation of two-level values accurate to Van Vleck correction is a correlation coefficient of these values.

Solar Radio Observations of the Proton Event of 1971 January 24

1972 ◽  
Vol 2 (2) ◽  
pp. 103-105 ◽  
Author(s):  
I. D. Palmer ◽  
S. F. Smerd ◽  
A. C. Riddle
Keyword(s):  
Field Line ◽  
Solar Radio ◽  
Rare Events ◽  
Ground Level ◽  
Single Frequency ◽  
Proton Event ◽  
Radio Observations ◽  
Neutron Monitors ◽  
The Earth ◽  
Radio Coverage

On 1971 January 24 a 3B flare at 18° N., 49° W. was associated with the acceleration of protons to relativistic energies; it was one of the rare events recorded by ground-level neutron monitors. Excellent radio coverage was obtained with single-frequency radiometers in the range 1000-9400 MHz, and at Culgoora with the 8-8000 MHz spectrograph and the 80 MHz radioheliograph. At the Earth relativistic protons and electrons arrived very promptly from the flare, whose site was near the foot of the nominal interplanetary field line which connects to the Earth.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

scholarly journals Numerical Simulation on Spatial-Frequency Domain Imaging for Estimating Optical Absorption and Scattering Properties of Two-Layered Horticultural Products

2021 ◽  
Vol 11 (2) ◽  
pp. 617
Author(s):  
Dong Hu ◽  
Yuping Huang ◽  
Qiang Zhang ◽  
Lijian Yao ◽  
Zidong Yang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Optical Property ◽  
Optical Absorption ◽  
Spatial Frequency ◽  
Estimation Accuracy ◽  
Property Estimation ◽  
Spatial Frequencies ◽  
Stepwise Method ◽  
Horticultural Products ◽  
Layered Samples

Spatial-frequency domain imaging (SFDI) is a wide-field, noncontact, and label-free imaging modality that is currently being explored as a new means for estimating optical absorption and scattering properties of two-layered turbid materials. The accuracy of SFDI for optical property estimation, however, depends on light transfer model and inverse algorithm. This study was therefore aimed at providing theoretical analyses of the diffusion model and inverse algorithm through numerical simulation, so as to evaluate the potential for estimating optical absorption and reduced scattering coefficients of two-layered horticultural products. The effect of varying optical properties on reflectance prediction was first simulated, which indicated that there is good separation in diffuse reflectance over a large range of spatial frequencies for different reduced scattering values in the top layer, whereas there is less separation in diffuse reflectance for different values of absorption in the top layer, and even less separation for optical properties in the bottom layer. To implement the nonlinear least-square method for extracting the optical properties of two-layered samples from Monte Carlo-generated reflectance, five curve fitting strategies with different constrained parameters were conducted and compared. The results confirmed that estimation accuracy improved as fewer variables were to be estimated each time. A stepwise method was thus suggested for estimating optical properties of two-layered samples. Four factors influencing optical property estimation of the top layer, which is the basis for accurately implementing the stepwise method, were investigated by generating absolute error contour maps. Finally, the relationship between light penetration depth and spatial frequency was studied. The results showed that penetration depth decreased with the increased spatial frequency and also optical properties, suggesting that appropriate selection of spatial frequencies for a stepwise method to estimate optical properties from two-layered samples provides potential for estimation accuracy improvement. This work lays a foundation for improving optical property estimation of two-layered horticultural products using SFDI.

Harmonic basis functions for spatial coding in the cat striate cortex

1989 ◽  
Vol 3 (4) ◽  
pp. 351-363 ◽  
Author(s):  
V. D. Glezer ◽  
V. V. Yakovlev ◽  
V. E. Gauzelman
Keyword(s):  
Spatial Frequency ◽  
Striate Cortex ◽  
Weighting Function ◽  
Discrete Distribution ◽  
Basis Functions ◽  
Spatial Coding ◽  
Central Visual Field ◽  
Spatial Frequencies ◽  
The Absolute ◽  
Number Of Cycles

AbstractThe number of subregions in the activity profiles of simple cells varies in different cells from 2–8; that is, the number of cycles in the weighting function varies from 1–4. The distribution of receptive-field (RF) sizes at eccentricities of 0-6 deg are clustered at half-octave intervals and form a discrete distribution with maxima at 0.62, 0.9, 1.24, 1.8, 2.48, and 3.4 deg. The spatial frequencies to which the cells are tuned are also clustered at half-octave intervals, forming a discrete distribution peaking at 0.45, 0.69, 0.9, 1.35, 1.88, 2.7, 3.8, and 5.6 cycles/deg. If we divide the RF sizes by the size of the period of the subregions, then the average indices of complexity (really existing) or the number of cycles in the weighting function form (after normalization) the sequences: 1, 1.41, 2.0, 2.9, 4.15.The relation between the bandwidth of the spatial-frequency characteristic and the optimal spatial frequency is in accordance with predictions of the Fourier hypothesis. The absolute bandwidth does not change with the number of cycles/module. This means that inside the module the absolute bandwidth does not change with the number of the harmonic. The results allow us to suggest the following. A module of the striate cortex, which is a group of cells with RFs of equal size projected onto the same area of central visual field, accounts for the Fourier description of the image. The basis functions of the module are composed of four harmonics only, irrespective of size and position of the module.Besides linear cells (sinusoidal and cosinusoidal elements), the module contains nonlinear cells, performing a nonlinear summation of the responses of sinusoidal and cosinusoidal elements. Such cells are characterized by an index of complexity which is more than the number of cycles in the weighting function and by marked overlap of ON and OFF zones. The analysis of organization suggests that the cells can measure the amplitude and phase of the stimulus.

scholarly journals Nonlinear analysis of decimetric solar bursts

2009 ◽  
Vol 5 (S264) ◽  
pp. 279-281
Author(s):  
Reinaldo R. Rosa ◽  
Mauricio J. A. Bolzan ◽  
Francisco C. R. Fernandes ◽  
H. S. Sawant ◽  
Marian Karlický
Keyword(s):  
Solar Radio ◽  
Inhomogeneous Plasma ◽  
Active Regions ◽  
Singularity Spectrum ◽  
Frequency Range ◽  
Radio Emissions ◽  
Magnetic Structures ◽  
Fine Structures ◽  
Solar Bursts ◽  
Solar Radio Emissions

AbstractThe solar radio emissions in the decimetric frequency range (above 1 GHz) are very rich in temporal and spectral fine structures due to nonlinear processes occurring in the magnetic structures on the corresponding active regions. In this paper we characterize the singularity spectrum, f(α), for solar bursts observed at 1.6, 2.0 and 3 GHz. We interpret our findings as evidence of inhomogeneous plasma turbulence driving the underlying plasma emission process and discuss the nonlinear multifractal approach into the context of geoeffective solar active regions.

Spatial-frequency and orientation tuning in psychophysical end-stopping

1998 ◽  
Vol 15 (4) ◽  
pp. 585-595 ◽  
Author(s):  
CONG YU ◽  
DENNIS M. LEVI
Keyword(s):  
Spatial Frequency ◽  
Frequency Tuning ◽  
Spatial Filter ◽  
Orientation Tuning ◽  
Maximal Strength ◽  
Facilitation Effect ◽  
Spatial Filters ◽  
Spatial Frequency Tuning ◽  
Spatial Frequencies ◽  
Wide Range

A psychophysical analog to cortical receptive-field end-stopping has been demonstrated previously in spatial filters tuned to a wide range of spatial frequencies (Yu & Levi, 1997a). The current study investigated tuning characteristics in psychophysical spatial filter end-stopping. When a D6 (the sixth derivative of a Gaussian) target is masked by a center mask (placed in the putative spatial filter center), two end-zone masks (placed in the filter end-zones) reduce thresholds. This “end-stopping” effect (the reduction of masking induced by end-zone masks) was measured at various spatial frequencies and orientations of end-zone masks. End-stopping reached its maximal strength when the spatial frequency and/or orientation of the end-zone masks matched the spatial frequency and/or orientation of the target and center mask, showing spatial-frequency tuning and orientation tuning. The bandwidths of spatial-frequency and orientation tuning functions decreased with increasing target spatial frequency. At larger orientation differences, however, end-zone masks induced a secondary facilitation effect, which was maximal when the spatial frequency of end-zone masks equated the target spatial frequency. This facilitation effect might be related to certain types of contour and texture perception, such as perceptual pop-out.

Investigation of the Influence of the Earth Ionosphere on the Radio Wave Propagation in the High-Frequency Range

2019 ◽  
Vol 64 (8) ◽  
pp. 740-746 ◽  
Author(s):  
Yu. I. Bova ◽  
A. S. Kryukovskii ◽  
B. G. Kutuza ◽  
D. S. Lukin
Keyword(s):  
Wave Propagation ◽  
Radio Wave ◽  
High Frequency ◽  
Radio Wave Propagation ◽  
High Frequency Range ◽  
Frequency Range ◽  
The Earth

scholarly journals Contrast thresholds reveal different visual masking functions in humans and praying mantises

2017 ◽  
Author(s):  
Ghaith Tarawneh ◽  
Vivek Nityananda ◽  
Ronny Rosner ◽  
Steven Errington ◽  
William Herbert ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Motion Detection ◽  
Visual Masking ◽  
High Spatial Frequency ◽  
Visual Noise ◽  
Frequency Noise ◽  
Detection Systems ◽  
Spatial Frequencies ◽  
Summary Statement ◽  
Contrast Thresholds

AbstractRecently, we showed a novel property of the Hassenstein-Reichardt detector: namely, that insect motion detection can be masked by “invisible” noise, i.e. visual noise presented at spatial frequencies to which the animals do not respond when presented as a signal. While this study compared the effect of noise on human and insect motion perception, it used different ways of quantifying masking in two species. This was because the human studies measured contrast thresholds, which were too time-consuming to acquire in the insect given the large number of stimulus parameters examined. Here, we run longer experiments in which we obtained contrast thresholds at just two signal and two noise frequencies. We examine the increase in threshold produced by noise at either the same frequency as the signal, or a different frequency. We do this in both humans and praying mantises (Sphodromantis lineola), enabling us to compare these species directly in the same paradigm. Our results confirm our earlier finding: whereas in humans, visual noise masks much more effectively when presented at the signal spatial frequency, in insects, noise is roughly equivalently effective whether presented at the same frequency or a lower frequency. In both species, visual noise presented at a higher spatial frequency is a less effective mask.Summary StatementWe here show that despite having similar motion detection systems, insects and humans differ in the effect of low and high spatial frequency noise on their contrast thresholds.

scholarly journals Elaborate pupils in skates may help camouflage the eye

2018 ◽  
Author(s):  
Sean Youn ◽  
Corey Okinaka ◽  
Lydia M Mäthger
Keyword(s):  
Light Intensity ◽  
Spatial Frequency ◽  
Experimental Evidence ◽  
Pupillary Response ◽  
Pupil Dilation ◽  
Primary Factor ◽  
Natural Substrate ◽  
Spatial Frequencies ◽  
Pupillary Responses ◽  
Changing Light

AbstractThe little skate Leucoraja erinacea has elaborately shaped pupils, whose characteristics and functions have not been studied extensively. It has been suggested that such pupil shapes may camouflage the eye; yet, no experimental evidence has been presented to support this claim. Skates are bottom-dwellers that often bury into the substrate with their eyes protruding. If these pupils serve any camouflage function, we expect there to be a pupillary response related to the spatial frequency (“graininess”) of the background against which the eye is viewed. Here, we tested whether skate pupils dilate or constrict in response to background spatial frequency. We placed skates on background substrates with different spatial frequencies and recorded pupillary responses at three light intensities. In experiment 1, the skates’ pupillary response to three artificial checkerboards of different spatial frequencies was recorded. Skates responded to changing light intensity with pupil dilation/constriction; yet, their pupils did not change in response to spatial frequency. In experiment 2, in which skates could bury into three natural substrates with different spatial frequencies, such that their eyes protruded above the substrate, the pupils showed a subtle but statistically significant response to changes in substrate spatial frequency. Given the same light intensity, the smaller the spatial frequency of the natural substrate, the more constricted the pupil. While light intensity is the primary factor determining pupil dilation, these experiments are the first to show that pupils also change in response to background spatial frequency, which suggests that the pupil may aid in camouflaging the eye.

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