scholarly journals VLF Emissions With Banded Structure in the 16‐ to 39‐kHz Frequency Range Measured by a High‐Latitude Ground‐Based Receiver

2019 ◽  
Vol 46 (24) ◽  
pp. 14214-14222
Author(s):  
Edith L. Macotela ◽  
František Němec ◽  
Jyrki Manninen ◽  
Ondřej Santolík ◽  
Ivana Kolmašová ◽  
...  
Keyword(s):  
High Latitude ◽  
Frequency Range ◽  
Banded Structure ◽  
Vlf Emissions

scholarly journals In connection with identification of VLF emissions before L'Aquila earthquake

2012 ◽  
Vol 12 (4) ◽  
pp. 1009-1015 ◽  
Author(s):  
M. K. Kachakhidze ◽  
Z. A. Kereselidze ◽  
N. K. Kachakhidze ◽  
G. T. Ramishvili ◽  
V. J. Kukhianidze
Keyword(s):  
Electromagnetic Emission ◽  
Retrospective Data ◽  
L’Aquila Earthquake ◽  
Frequency Range ◽  
The Earth ◽  
Atmosphere System ◽  
Data Application ◽  
Electromagnetic Oscillations ◽  
Vlf Emissions ◽  
Geomagnetic Perturbations

Abstract. The present paper deals with an attempt to check the theoretical model of self-generated seismo-electromagnetic oscillations of LAI system on the basis of retrospective data. Application of the offered simple model enables one to explain qualitatively the mechanism of VLF electromagnetic emission initiated in the process of an earthquake preparation. Besides, the model enables us to associate telluric character geoelectric and geomagnetic perturbations incited by rock polarization and self-generated electromagnetic oscillations of lithosphere-atmosphere system. L'Aquila earthquake taken as an example to isolate reliably the Earth VLF emission from the magnetospheric electromagnetic emission of the same frequency range, MHD criterion is offered together with geomagnetic activity indexes. On the basis of the considered three earthquakes, according to the opinion of authors the model of self-generated seismo-electromagnetic oscillations of the LAI system will enable us to approach the problem of resolution of earthquake prediction with certain accuracy.

scholarly journals Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

2010 ◽  
Vol 28 (9) ◽  
pp. 1761-1775 ◽  
Author(s):  
N. V. Yagova ◽  
V. A. Pilipenko ◽  
L. N. Baransky ◽  
M. J. Engebretson
Keyword(s):  
High Latitude ◽  
Spectral Power ◽  
Quantitative Description ◽  
Auroral Oval ◽  
Broadband Noise ◽  
Frequency Range ◽  
Spectral Slope ◽  
Geomagnetic Disturbances ◽  
Spectral Moments ◽  
Spectral Parameters

Abstract. We analyze spectral parameters of the geomagnetic disturbances within the 1–4 mHz (Pc5/Pi3) frequency range for 29 observatories from polar to auroral latitudes. The main object of this study is the broadband (noise) background under quiet and moderately disturbed conditions. To obtain a quantitative description of background high-latitude long period ULF activity the log-log dependence of the spectral power on frequency is expanded over Legendre polynomials, and the coefficients of this expansion (spectral moments) are used to describe the most common features of these spectra. Not only the spectral power, but also the spectral slope and higher spectral moments, averaged over relatively long time intervals, demonstrate a systematic dependence on corrected geomagnetic (CGM) latitude, Φ, and magnetic local time, MLT. The 2-D distributions of the spectral moments in Φ-MLT coordinates are characterized by existence of structures, narrow in latitude and extended in MLT, which can be attributed to the projections of different magnetospheric domains. Spatio-temporal distributions of spectral power of elliptically (P-component) and randomly (N-component) polarized signal are similar, but not identical. The N-component contribution to the total signal becomes non-negligible in regions with a high local activity, such as the auroral oval and dayside polar cusp. The spectral slope indicates a larger relative contribution of higher frequencies upon the latitude decrease, probably, as a result of the resonant effects in the ULF noise. The higher spectral moments are also controlled mostly by CGM latitude and MLT and are fundamentally different for the polarized and non-polarized components. This study is a step towards the construction of an empirical model of the ULF wave power in Earth's magnetosphere.

Correlations between very low frequency chorus bursts and impulsive magnetic variations at L ~ 4.5

1981 ◽  
Vol 59 (8) ◽  
pp. 1034-1041 ◽  
Author(s):  
S. Kokubun ◽  
K. Hayashi ◽  
T. Oguti ◽  
K. Tsuruda ◽  
S. Machida ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Range ◽  
Conductivity Enhancement ◽  
Very Low Frequency ◽  
Close Relationship ◽  
Magnetic Pulsations ◽  
Whistler Mode Waves ◽  
Short Time ◽  
Vlf Emissions ◽  
Vlf Waves

Coordinated observations of aurora, ULF, and VLF waves were made at 13 stations in Canada in January and February, 1980. The analysis of simultaneous ULF and VLF data obtained at Park Site (L = 4.4) revealed a close relationship between irregular magnetic pulsations and VLF emissions in the frequency range of 1.5–5 kHz. One-to-one correlations were observed between VLF chorus bursts and impulsive magnetic variations, called magnetic impulses, during sub-storms of Kp ≥ 4+ on the local morning-to-noon side. VLF chorus bursts consist of discrete risers of 0.1–0.3 s duration. It is found that magnetic impulses with a rise time of 0.5–1 s and with a duration of ~2 s coincide with the occurrence of VLF riser groups of a similar duration within ~2 s. This short time difference strongly suggests that magnetic impulses are caused by a conductivity enhancement due to electron precipitation induced by whistler mode waves.

scholarly journals New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone

2012 ◽  
Vol 30 (12) ◽  
pp. 1655-1660 ◽  
Author(s):  
J. Manninen ◽  
N. G. Kleimenova ◽  
O. V. Kozyreva
Keyword(s):  
Temporal Dynamics ◽  
Low Frequency ◽  
Auroral Zone ◽  
Spectral Structure ◽  
Geomagnetic Pulsations ◽  
Frequency Range ◽  
Theoretical Investigations ◽  
New Type ◽  
Periodic Signals ◽  
Vlf Emissions

Abstract. A new type of the series of quasi-periodic (QP) very low frequency (VLF) emissions in frequency range of 1–5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3) during the Finnish VLF campaign (held in December 2011). At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0–1), although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2–3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF). This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

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.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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