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Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.


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Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the trend in variation of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geOMagnetic footprints on the D region characteristics.

10 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a theory of propagation of low-frequency radio waves generated by very low frequency (VLF) emissions and a classification of observed VLF noise.
Abstract: CONTENTS Introduction 743 1 Observational Data on Natural Low-Frequency Radio Emission 744 a) Whistlers 745 Dispersion Long and short whistlers Multiple whistlers Nose whistlers Discharges that generate whistlers Experimental data on the trajectories of whistlers Systematic variations of properties of whistlers Observation of whistlers in the IGY program b) Very Low Frequency Emissions 749 Systematic classification of observed VLF noise Certain features of discrete radiation Method of propagation Tendency to form horizontal or gliding tones Connection with magnetic activity Comparison of steady states (hissing) with transients (discrete radiation) 2 Theory of Propagation of Low-Frequency Radio Waves Generation of VLF Emissions 751 Principal initial relations Group velocity and determination of trajectories Allowance for ion motion Interaction of normal waves Absorption Mechanisms of generation of VLF emissions 3 Low Frequency Radio Waves and Investigation of the Upper Atmosphere 761 Conclusion 763 Cited Literature 763

10 citations

Journal ArticleDOI
28 Aug 2014
TL;DR: It was concluded that the individual components in the VLF structure can demonstrate reciprocal relationships at a load among themselves and in the LF/HF ratio, and play an adaptive role in the mechanisms of autonomic provision.
Abstract: Researched physiological mechanisms of development of orthostatic tachycardia syndrome (POTS) on the basis of a complex spectral structure analysis of heart rate variability (HRV), its nonlinear behavior in relationship to energy oscillations, baroreflex and parasympathetic activity. There were several stages of research. The first stage: created the method of spectral analysis of individual components of Very Low Frequency (VLF). On the basis of comparative Fast Furrier Transform data with Welch filters, autoregression, continuous wavelet analysis and Hilbert–Huang transform, for the first time it was shown that VLF has separate 200, 100 and 50 s oscillations (VLF200, VLF100, VLF50). The second stage: for evaluation of physiological properties of separate oscillations, was analyzed VLF structure in three groups of patients (100 subjects): with a predominance of parasympathetic activity (HF) in the HRV spectrum; with a dominance of 10 s oscillations (LF); with a severe depression of energy in all components of the spectrum. It was established that the individual components of VLF (VLF100 and VLF50) have a certain stability and partial independence from the changes of peripheral autonomic indices (LF/HF) at loads of low intensity. The third stage: at an active orthostatic test, 20 subjects with orthostatic tachycardia were researched in a comparison to a control group of 20 subjects without tachycardia. Analyzed the specifics of the VLF structure (VLF100 and VLF50) alone and in a conjunction with the LF and HF, as well as heart rate and blood pressure in subjects with orthostatic tachycardia with a predominance of parasympathetic activity at functional tests of low intensity (seven-test, deep breathing) and at an active orthostatic test. Based on these studies it was concluded that the individual components in the VLF structure (VLF100, VLF50) can demonstrate reciprocal relationships at a load among themselves and in the LF/HF ratio, and play an adaptive role in the mechanisms of autonomic provision. Revealed the importance of VLF and its components 100 and 50 s oscillations at an orthostatic test in the prognosis of orthostatic tachycardia development. In patients with dysautonomia at high level of VLF100 power, or high VLF50 indices, tachycardia did not develop. In this case, VLF and its component parts did an important adaptive function and conversely, the low VLF50 indices contribute to orthostatic tachycardia. In the proposed model of the descending neurosomatic control of autonomic regulation of HRV a very important role plays both neurogenic ways of regulation, and neuro-hormonal-metabolic ways, manifested in the complex VLF structure. Regarded the choice of ways and optimal neurosomatic models of regulation at POTS.

10 citations

Journal ArticleDOI
TL;DR: In this paper, the authors performed a statistical study of low frequency (LF) auroral hiss recorded at South Pole Station in 2004, 2005, and 2007, and showed that dayside LF hiss almost always extends to the VLF range and is often associated with active aurora.
Abstract: [1] We performed a statistical study of low frequency (LF) auroral hiss recorded at South Pole Station in 2004, 2005, and 2007, and very low frequency (VLF) hiss recorded in 2000–2008. As expected, most auroral hiss occurs in the pre-midnight sector. However, there is a secondary peak in occurrence in the pre-noon sector (1000–1530 UT; ∼ 0630–1200 magnetic local time (MLT)) and somewhat more events occur in the post-noon sector (1530–2100 UT; ∼ 1200–1730 MLT), with a null in occurrence around noon MLT. Individual dayside events appear similar to nightside hiss, but statistically they do not extend to as high frequencies. Solar wind discontinuities or impulses on the magnetopause are not correlated with these events. All-sky camera, photometer, magnetometer, riometer, and VLF receiver data show that dayside LF hiss almost always extends to the VLF range and is often associated with active aurora. Examination of interplanetary magnetic field (IMF), substorm conditions, and Kp/AE/QI indices at times of dayside hiss suggests differences between the pre-noon and post-noon events: pre-noon events are associated with IMF By 0. The correlation between pre-noon events and By < 0 may arise because under those conditions, the pattern of field-aligned currents (FACs) shifts to later magnetic local times, causing upward FACs to be dominant during pre-noon hours at 74°, the invariant latitude of the South Pole. Unlike pre-noon events, post-noon events are more often associated with substorm activity on the nightside and favor elevated Kp indices, suggesting a connection of post-noon events to nightside activity.

10 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202232
202156
202048
201942
201852